Thirty children infected with human immunodeficiency virus (HIV) (18 P1 and 12 P2, according to the classification system of the Centers for Disease Control) and 54 noninfected children were evaluated for lactose malabsorption with use of the hydrogen breath test after different lactose loads. Lactose malabsorption after load of 2 g/kg occurred in 75% of P2, 67% of P1, and in 46% of noninfected children. With a lower lactose load (1 g/kg), the prevalence of malabsorption was significantly higher among P2 children than P1 and noninfected cases. A similar figure was obtained after the lowest load (0.5 g/kg). Infected children with lactose malabsorption were significantly younger than noninfected malabsorbers (mean age +/- SD; 50.3 +/- 22 vs. 63.5 +/- 20.9 months) when the load of 2 g/kg was used. The use of lower lactose loads seems to be helpful in finding the dose that can be tolerated. This finding could have nutritional importance and could lead to better dietary management.