The clinical and serological responses to attenuated measles virus vaccine were compared in 35 severely malnourished and 35 well-nourished children. A third group of severely malnourished children, who received an injection of vitamin B12, served as controls. The children were observed for three weeks following vaccination. Paired sera were collected from each child before and after administration of the vaccine or vitamin B12 and measles antibody titres were estimated using HAI technique. The malnourished children who received measles vaccine developed higher fever of longer duration and had more lower respiratory tract disease than the other two groups but had fewer skin rashes than the well-nourished group. Sero-conversion rates were 96% had 92.6% in the malnourished and well-nourished vaccinated children, respectively. Antibody titres were lower in children who had marasmic/kwashiorkor than in the marasmic children.