We studied the growth of comparable groups of children with light to moderate Schistosoma haematobium infections who received a single dose of metrifonate (MT, 10 mg/kg), praziquantel (PR, 40 mg/kg), or a placebo (PL). Children were re-examined 8 months later. The MT and PR groups gained significantly more than the placebo group in weight, percent weight for age, percent weight for height, arm circumference, and in triceps and subscapular skinfold thicknesses. The MT and PR groups did not differ significantly from each other. The placebo group showed statistically significant decreases or no change between exams in percent weight for age, percent weight for height, percent arm circumference, and both skinfold thicknesses; the MT and PR groups exhibited highly significant increases in these parameters (P less than 0.0002). The intensity of S. haematobium infection had decreased significantly in both the MT and PR groups, but especially in the PR group. Multiple regression analyses showed that a decrease in the intensity of S. haematobium infection was by far the most important predictor of growth rate after treatment for all 5 anthropometric measures tested; decreases in the intensity of hookworm infection was also significant for 2 of the 5 measures.