Anticardiolipin antibodies (ACA) were determined in 72 heavily transfused haemophiliacs, 43 HIV-positive and 29 HIV-negative. The presence of ACA was detected in 10 patients, all of them infected by HIV: 8 in CDC II, 1 in CDC III and 1 in CDC IV. The comparison with alterations of other laboratory markers in HIV-infected patients did not show any statistically significant difference between ACA-negative and -positive patients. In summary, ACA were found only in HIV-infected haemophiliacs. In this subgroup of patients the presence of ACA was not associated with progression to AIDS.