To investigate leukocyte inhibitory factor(LlF) production and circulating immune complexes (CIC) in leprosy, peripheral blood mononuclear cells (PBMC) from 61 patients and sera from 6O patients were tested. The results indicate that there is a defect in LlF production in the lepromatous (LL) or borderline lepromatous (BL) types compared to the tubrculoid (TT) type (mean migration index=66.O ± 16.O in LL 61.1 ± 15.3 in BL, 51.9 ± 11.2 in TT) (p < 0.05). The number of patients with positive CIC was higher among the LL patents (30%) than the TT patients (20%). There was also positive correlation between the bacterial index (Bl) and the CIC level (r=0.46, p < 0.05). The correlation between CIC and LIF in LL patients and the possibility (p=0.06) that the inuease m CIC may account for the decrease in LIF production in LL patients and vice versa are discussed.