Studies have shown that estrogens and progestogens can cause immuno-depression. Oral contraceptives (OCs) have also been linked with viral and urinary tract infections. In developing countries, women have higher risks of developing these infections because of undernutrition and anemia. This study evaluates cell-mediated immunity (CMI) and one parameter of hormonal immunity--serum hemolytic complement--in undernourished Indian women using OCs. The study population consisted of a random sample of urban women of low income status, between 20 and 30 years of age, mean weight of 45.2 kg. and mean height of 151.2 cm., and mean hemoglobin level of 13.2 g/dl (none had hemoglobin levels below 8 g/dl). 52 of the women were taking OCs (150/ug. of d. norgestrol and either 30 or 50/ug. ethinyl estradiol). The T and B lymphocytes, hemolytic complement in serum (CH50), PHA-induced lymphocyte transformation (PILT) were measured. Results revealed a wide scatter of values in all 4 parameters--% of T cells; % of B cells; 3H-thymidine incorporation, and CH50 levels even in the control group. No significant differences in % of B and T lymphocytes subpopulation or PILT were observed between OC users and the control group. CH50 levels were significantly lower, however, in OC users. Generally, clinical experience of pill users suggests that there is no need for undue concern for potential immune-associated problems in OC users.