The relationships between Ascaris lumbricoides worm burden, growth status, general delayed cutaneous hypersensitivity (DCH) response, and plant anthelmintic use were investigated in a 12-mo prospective survey of 663 children, 4-10 yr old, living in the Ranomafana rainforest, Madagascar. Initial fecal examinations revealed prevalences of 93% for A. lumbricoides, 55% for Trichuris trichuria, and 27% for hookworm. After anthelmintic treatment and a 12-mo reinfection period, 428 of the children participated in worm expulsion studies using pyrantel pamoate, revealing an overdispersed A. lumbricoides worm population, mean = 19.2 (SD = 20.4). Malnutrition was common with 72% of the children growth stunted, 61% underweight, and 6% wasted. The children were also skin tested to recall antigens for DCH, with 94% reacting. The DCH immune response was significantly decreased in the malnourished children; however, DCH was not reduced in relation to increasing worm intensity. Growth status, growth velocity, and triceps skinfold did not vary significantly in relation to A. lumbricoides worm burden. Traditional plant anthelmintic treatment was effective in significantly reducing worm intensity. This study indicates that, in human communities where the children are predominately stunted, A. lumbricoides does not aggregate in the most malnourished or immunodepressed children.