Based upon 10 months of field work with the uniformed police patrol of a large West Coast city, and on psychiatric records of the hospital receiving all police referrals, the report identifies five types of situations which usually result in a person's being taken to the hospital: evidence of suicide, distortions of normal physical appearance, highly agitated activity (especially when manifested in violent acts), persons creating a public nuisance, and upon request from physicians or persons in some sort of instrumental relationship. Nonetheless, there are encounters in which officers explicitly recognize signs of mental illness and treat it as the primary business at hand, but because no official action is taken, these incidents are not officially recorded. By far, the largest number of police encounters with mentally ill persons involve trying to find competent persons to whom they may relinquish the care of the patient. In these situations, no other social agency, either legal or medical, participates and the police act as the terminal, all-purpose remedial agent. Although police training and literature include references to the handling of mentally ill persons, officers are not instructed in actual techniques. With no more to go on than the maxims of kindness and caution, officers tend to fall back on being formally correct. Seasoned officers invariably remove the patient from the immediate context in which they are found. In direct dealings with the patient, the officer tries to establish and maintain the pretense of a normal conversational situation. This practice of 'psychiatric first aid' is representative of the overall involvement of the police with mental illness. A significantly less frequent type of activity practiced by a limited number of foot patrol officers can be best characterized as continuing care. These officers, especially when they work in a slum, know some mentally ill persons with whom they have established a more or less regularized pattern of meeting each other. These encounters, as in the practice of 'psychiatric first aid,' tend to confine and disregard pathological elements and to reduce matters to mundane aspects. The result is that proper understanding of recorded police interventions hinges on the knowledge of cases for which there is no official record. Nineteen footnotes are provided.