The interference of chlorpromazine (CPZ) and several preincubated CPZ metabolites on the lymphocyte absorption of antibodies directed against HLA-A1 and other nonrelated HLA specificities were investigated. Both CPZ and metabolites 7-OH-, Nor1-, and Nor2-CPZ were found to interfere with the specific absorption of anti-HLA-A1 antibodies. The meaning of such a result is discussed.