Sera from 154 hemophiliacs, including 132 with hemophilia A and 22 with hemophilia B, were examined for antibodies against human T cell lymphotropic virus type III (HTLV-III) and type I by strip radioimmunoassay based on the Western blotting technique. Sixty-two patients lived in Kyushu, a known endemic area of HTLV-I and 92 patients lived in Tokyo, a nonendemic area of HTLV-I. Results showed a prevalence of HLTV-III antibodies of 64.5% in Kyushu and of 57.6% in Tokyo. There were no significant differences between these two groups. Helper/suppressor (T4/T8) ratios of seropositive patients were 0.69 ± 0.41 and those of seronegative patients were 1.05 ± 0.56. Ratios of both groups were lower than those of normal healthy people (1.35 ± 0.45). Our findings confirmed that hemophiliacs living in an HTLV-I endemic area and those living in a nonendemic area in Japan equally possessed antibodies to HTLV-III. Low T4/T8 ratios and increases of serum IgG and IgM levels were found even in seronegative hemophiliacs.