Serological testing of waste bloods revealed that 25 (7%) of 350 acutely ill psychiatric inpatients had HIV infection. Eight of the 10 HIV-positive patients whose serological status was not recorded on admission were discharged with their status still unrecorded and presumably undetected. Thirty-nine (51%) of the 77 inpatients with HIV-related risk behaviors identified on admission were discharged with no record of their having been serologically tested before or during hospitalization.