Therapists ? psychiatrists, psychotherapists, psychiatric social workers and other mental health professionals ? are as much part of the New York landscape as hot dog vendors. And they have discovered, sometimes the hard way, that delving deeply into people’s feelings can be dangerous. As police detectives searched on Wednesday for a man who killed a psychologist with a meat cleaver and other knives ? and seriously injured another therapist, who heard their struggle from his nearby office and went to help ? therapists said they had learned to develop their own physical and psychological defenses against violence.

“You do this work long enough, and you pretty much see everything, even in Manhattan,” said Dr. Robert H. Reiner, the executive director of Behavioral Associates, a private outpatient psychotherapy institute on the Upper East Side.

The identity of the attacker in Tuesday’s killing was not known, and the police said it was not clear if he was a patient or a patient’s relative, or if he had some other connection to the victims.

Still, therapists said they recognized the inherent risk in treating some types of patients. Dr. Reiner said most of the patients he saw, in six to eight “intake interviews” a day, had anxiety disorders that carried a low risk of violence. But every so often, he realizes that a patient has a severe psychosis.

“Often as not, it’s someone who’s walking around like you and me, and the psychosis is well disguised, and I realize they could be dangerous,” Dr. Reiner said. “And I look at the window and I think, ‘How quick can I get out?’ Every psychotherapist in an urban area knows this feeling.”

Just how much violence is directed at therapists is an open question. Of a dozen therapists in private practice in New York City who were interviewed on Wednesday, only one said he had ever seen violence in his office, and he was not the target: A father and son came to blows, he said.

But when Christina E. Newhill, an associate professor at the University of Pittsburgh, surveyed 1,129 therapeutic workers nationwide in 2003, 58 percent said they had had to deal with violence, though only 24 percent of those said they had actually been attacked. Twenty-five percent of those who had to deal with violence said clients had damaged or destroyed property, while half said the episodes did not go beyond threats.

Gary Arthur, a professor emeritus at Georgia State University, surveyed all 6,400 licensed therapists in Georgia in 2001. Of the 1,132 who responded, 14 had been shot at, 6 attacked with a knife, 209 pushed or shoved, 112 slapped and 87 hit by objects thrown at them. None of the therapists who said they had been shot at were struck by the bullets, he said.

“The results were scary,” he said in an interview. “Our profession remains very high on the list for risk of danger.”

Twice in his years as a psychologist, Dr. Alan Hilfer, now the chief psychologist at Maimonides Medical Center in Brooklyn, has had to deal with violent patients: once when a father and son got into a knock-down-drag-out brawl in his consultation room, and once when a teenager threw a paperweight at the therapist in the next office.

Dr. Hilfer said therapists were not taught precautions ? like where to position oneself during a consultation ? during training.

He recalled being asked, early in his career, to interview a man seeking treatment. “I allowed him to come between me and the door” in the consultation room, Dr. Hilfer said. “He became agitated and threatening, and I couldn’t get out of the room.”

In some group practices or in hospitals, he said, therapists leave the door open during a first encounter with a patient. They also alert a colleague, who listens for sounds of a disturbance. Dr. Newhill teaches a class that tells prospective therapists how to do risk assessments and handle patients who turn violent. In a telephone interview, she said she started the class because of a murder in California in 1989. A therapist at a mental health clinic in Santa Monica was stabbed 31 times in her office by a patient, a street person who Dr. Newhill said was delusional.

“Violence is an interaction between the person and their environment,” she said, adding that the best predictor of future violence is a recent history of violence. She tells her students to work out, in advance, a plan that includes a way to signal for help. Some therapists install silent alarms. Others work out a phrase that lets a colleague know help is needed: “Please cancel my appointment for 3 o’clock” could mean “Call 911,” for example.

Dr. Reiner, of Behavioral Associates, said patients who turn violent had often “scoped things out in advance.” He said they would figure out whether a therapist worked alone or in an office with secretaries, other therapists or even video surveillance cameras.

But therapists who work by themselves, as many do in Manhattan, cannot turn to a colleague or a subordinate for assistance when a session degenerates.

“There is no warning system” for solo practitioners, Dr. Hilfer said. “We can try to use our clinical awareness and our knowledge of the patient, and if we are concerned about a patient, we will send them for a consult with someone. But in terms of protection, there’s none. It underscores the vulnerability that many of us understand.”