Production of leukocyte migration inhibition factor was measured in vitro with purified protein derivative and phytohemagglutinin in 14 marasmic infants 6 to 18 months of age. Twenty-seven well-nourished infants served as controls. All the children had received BCG vaccine in the neonatal period. Tuberculin reaction was positive in four of 14 of the marasmic infants and 13 of 27 of the controls. When leukocyte migration inhibition factor was induced with purified protein derivative, the four tuberculin positive malnourished subjects had a mean migration inhibition index of 55.7% which was significantly higher than the mean migration inhibition index of 38.2% in the tuberculin positive controls. In the tuberculin negative subjects the mean migration inhibition index was 24.7 and 16.6% in the marasmic and control groups, respectively. The difference was not statistically significant. Phytohemagglutinin-induced migration inhibition was comparable in malnourished and control infants. There was no correlation between leukocyte migration inhibition factor production and biochemical indices of iron nutrition, erythrocyte or serum folate, vitamin A, carotene, or serum zinc levels in either group. It is suggested the capacity of lymphocytes to produce leukocyte migration inhibition factor is unchanged in marasmus.