Between September 1987 and January 1988, blood samples from 796 consecutive new male inmates admitted to the Washington State correctional system were tested for HIV seropositivity. Only five were positive, yielding a seroprevalence of 0.6 percent. The second group of inmates, tested between October 1985 and September 1988, were identified for HIV testing through their own request, for clinical indications, or by court order. During the Open HIV seroprevalence study period, 1027 tests were performed on 968 inmates; 27 tests were positive in 26 inmates, for a 2.7 percent seroprevalence rate. The findings were similar to those in other States outside the major clusters of AIDS cases; the low seroprevalence in inmates is probably related to the low seroprevalence in the intravenous drug users in Washington State. The evidence suggests that educational programs increase the rate of inmate-initiated HIV testing, and that these efforts should be particularly emphasized among minority and female inmate populations. 2 tables, 2 figures, 7 references.