The apparent absorption of nitrogen (N), fat, and total energy from a rice and vegetable diet was measured in 13 children of similar nutritional status but infected with varying loads of Ascaris lumbricoides. Apparent N absorption was modestly decreased initially in subjects with heavy infections as compared to those with light infections (57.2% of intake versus 64.1% of intake, 0.05 < P < 0.1). After antihelminthic therapy there ws a significant improvement in apparent N absorption (P < 0.02), apparent N retention (P < 0.05), and apparent fat absorption (P < 0.05) for the group as a whole, particularly for those with heavy infections. Total energy absorption improved slightly, but not significantly, after treatment, and there was no change in xylose excretion tests. Treatment of ascariasis may be nutritionally advantageous for children with heavy worm burdens and marginal protein availability.