Anticardiolipin antibodies (ACA) and lupus-like anticoagulant (LLAC) have been studied in a group of 142 non-hospitalized and a group of 72 hospitalized HIV infected patients. We observed a variable frequency of ACA positivity ranging from 7.7% to 30.3% according to the groups of patients and the isotype of immunoglobulin fraction containing ACA activity. None of the patients investigated presented a prolongation of the activated partial thromboplastin time (APTT) compatible with the presence of a LLAC. Some patients presented a weak anticoagulant activity only detected by the tissue thromboplastin inhibition (TTI) test. No positive correlation was found between this latter test and ACA. We conclude that, like in syphilitic patients, ACA present in HIV infected patients are most often not associated with LLAC.