Antibody production in kwashiorkor and marasmic infants was studied by dividing them into three groups and giving the first group a single dose of trivalent live attenuated polio virus, the second group live attenuated measles virus and the third group diphtheriatoxoid. The production of antibodies was found to be deficient in PEM as compared to normals and diminished more in kwashiorkor than in marasmus cases. The individuals of the complement system were significantly lower in kwashiorkor than in normal controls. However, C3 was the only fraction which is significantly diminished in marasmic infants. The results are discussed and as a conclusion it is suggested that deficient production of antibodies and diminution in the complement system in PEM may explain the susceptibility of such infants to repeated attacks of infection.