Dioctahedral smectite, a non systemic antidiarrheal agent, is mucoprotective and absorbs enterotoxins and rotavirus as demonstrated in animal models. Smectite has been successfully used in various countries in children and adults with acute diarrhea. This study was to assess the efficiency of smectite associated with rehydration in infants with acute secretory diarrhea. Sixty-two hospitalized Thai infants, aged 1-24 months, with acute secretory diarrhea were randomly divided into 2 groups receiving (1) oral rehydration solution (ORS) (30 cases), (2) ORS and Smectite (3.6 g/day) (32 cases). Both groups were comparable for age, weight, nutritional status and duration of symptoms before treatment. All 62 infants received lactose free formula and chicken rice soup as the standard diet. Stool frequency, weight change and duration of diarrhea were recorded. The mean duration of diarrhea was 84.7 +/- 48.5 hours in group 1, and 43.3 +/- 25.1 hours in group 2 (p = 0.005). The number of infants with diarrhea was significantly lower in group 2 on Day 1 (p < 0.01) and Day 3 (p = 0.001); furthermore 27% of infants in group 1 and 3% in group 2 had still diarrhea on Day 5. The stool frequency and weight changes were not statistically different in the two groups. No major side effects were observed except two cases of vomiting and hardened stools. It is concluded that (1) Smectite shortens the course of acute secretory diarrhea in Thai infants; (2) smectite may reduce the occurrence of prolonged diarrhea; furthermore (3) in our study dioctahedral smectite was found to be safe in children aged 1 to 24 months.