Data are analyzed that describe the clinical work of representative samples of psychiatrists and clinical psychologists who practiced in one of 62 markets for mental health services in the United States during 1982 and 1983. For psychiatrists, intensity of treatment (ie, mean face-to-face treatment minutes per patient per month) varied from 107 to 368 minutes vs 124 to 283 minutes for psychologists. Multiple regression models explain these variations somewhat differently for each provider group. Whereas the patient's severity or stage of illness is explanatory for both psychiatrists and psychologists, only psychologists appear to alter intensity of treatment in response to local economic conditions. Psychiatrists have large diversified practices, whereas psychologists tend to treat fewer persons and the bulk of these have less severe mental and emotional conditions. Neither practitioner group appeared to provide services in excess of their perceptions of patient need. These and other important similarities and differences are explored, and the advantages of local market focus for examining relevant public policy issues are discussed.