One-hundred eighty-five Bangladeshi children age 1 1/2 to 8 yr with no Ascaris lumbricoides infection or with light, moderate, or heavy infection were randomly assigned to treatment or placebo groups, with treatment given in a double-blind fashion. The groups were comparable for nutritional and socioeconomic parameters. Treatment consisted of a single dose of piperazine citrate administered twice within a 2-wk period. The cure rates for the low, moderate and heavy A. lumbricoides infected subgroups were 53, 31 and 36%, respectively. With more severe infections, worm eradication was more difficult and the rate of reinfection after treatment was more rapid. The rate of reinfection was significantly different for the low A. lumbricoides infected treatment and placebo subgroups for 5 months after treatment, for the moderate treatment and placebo subgroups for 3 months after treatment, and for the heavy A. lumbricoides infected treatment and placebo subgroups there was a difference, although not significant, for 1 month after treatment. Anthropometric measurements were obtained for a period of 11 months. Analysis of covariance revealed no significant difference for change of weight, change of height, weight-for-age, weight-for-height, height-for-age, triceps, skinfold, midarm circumference, and the abdominal girth to chest circumference ratio between the treatment and placebo groups after drug administration. The results of this study do not support single dose worm therapy as a means to enhance growth.