Colostrum collected from 122 lactating women in India had mean IgA, IgG and IgM concn. 331, 17 and 58 mg/100 ml and mean total cell, lymphocyte and macrophage counts 2906, 813 and 1581/mm³. All those values decreased rapidly in milk during the first 7 days of lactation and thereafter gradually for the next 6 months. Relative ratios of the different Ig remained unaltered at all times during lactation. Lymphocyte count of colostrum increased significantly with parity, but Ig content was independent of parity. Total cell count (3450/mm³) in the colostrum of well-nourished mothers was significantly higher than that of the undernourished (2420/mm³) and had a positive relation to serum albumin. Cell count in the milk of the well-nourished group was higher at all periods of lactation. Ig contents were not remarkably different in the 2 groups. Dietary habits of the mothers had no effect on the cellular and humoral immunological measurements of colostrum.