To examine the prevalence and characteristics of the mentally disordered jail inmates, an exploratory search probe was conducted in a Pacific Northwest urban jail. The data base from which the sample was identified consisted of case records from the central intake and screening program. A total of 1,565 case records based on interviews with inmates were examined. The study sample generally reflected national trends in attributes of jail populations. Of the sample, 21 percent had been designated as mentally disordered. Since the jail functions as an alternative form of institutional care for mentally impaired persons whose behaviors violate community norms, it can provide a strategic base for diverting them systematically to more appropriate social care arrangements. Central intake and screening programs, established in a few jails, must be developed to facilitate such a process. Criminal justice personnel and community service providers must work together to identify and provide appropriate services that meet the differential treatment needs of mentally disordered inmates. 5 notes and 24 references