In developing countries, both marginal vitamin A status and intestinal helminths are common among children. Indonesian children (n = 309, 0.6-6.6 y), known to be infected with Ascaris lumbricoides, were randomized into six different treatment groups (A-F). The treatments included 210 mumol vitamin A supplement and a dose of 400 mg albendazole (5-propylthio-1H-benzimidazol-2-yl carbamic acid methyl ester) administered orally either at the same health visit (Groups B and F) or at different contact times during a 1-mo period (groups A, C, D and E). Vitamin A status was assessed both before and 3-4 wk after the treatments by the modified relative dose response (MRDR) test. Vitamin A supplementation was most important in improving the vitamin A status (P < 0.0001) of these children, whereas treatment for ascariasis alone (P = 0.370) and the statistical interaction between treatment for ascariasis and vitamin A (P = 0.752) were not. Serum retinol concentrations marginally improved (P = 0.051) in two of the groups that received vitamin A and albendazole but not in the third group that received vitamin A only. The MRDR test proved a better discriminator of the effects of these treatments on vitamin A status than changes in serum retinol concentrations.