Complement components of C1-C9 were estimated in children with protein-calorie malnutrition. The diagnosis of kwashiorkor and marasmus were based on clinical examination, anthropometric measurements and on biochemical estimations. The children were examined clinically and bacteriologically for any evidence of infection. All the complement components except C4 and C5 were significantly lower in children with protein-calorie malnutrition: of all the complement components C3 and C9 were the most severely depressed. C5 was the only complement component that was significantly higher in malnourished children than in normal children. Malnourished children with C-reactive protein in their serum had significantly lower values of C3 and C9 and higher values of C5 than malnourished children without C-reactive protein in their serum. During refeeding C3 was the first complement to show a significant rise. This was followed by C9. There was a fall in C5 concentration while there was no change in C4 concentration. The roles of infection, malnutrition and C-reactive protein on complement depletion are discussed.