Over a period of 20 months we identified 10 voluntary blood donors with indeterminate reactions in anti-HIV 1/2 EIA tests. Western blot (WB) patterns of 6 of these 10 donors showed isolated core antibodies (anti-p24), in 4 cases WB patterns were negative. After a median follow-up period of 58 weeks (range 12-93) we have not seen a case of typical seroconversion.