1. The amelioration of aflatoxicosis in broiler chickens was examined by feeding 2 concentrations of natural zeolite (clinoptilolite). Clinoptilolite (CLI), incorporated into the diet at 15 and 25 g/kg, was evaluated for its ability to reduce the deleterious effects of 2·5 mg total aflatoxin (AF; 76·40% AFB1, 16·12% AFB2, 6·01% AFG1 and 1·47% AFG in diet on growing broiler chicks from 1 to 21 d of age. A total of 360 broiler chicks were divided into 6 treatment groups (6 replicates of 10 broilers each): control, AF, CLI (15 g/kg), AF plus CLI (15 g/kg), CLI (25 g/kg), and AF plus CLI (25 g/kg). 2. Compared to controls, the AF treatment had significantly decreased body weight gain from week 1 onwards. The adverse effect of AF on food consumption (8·0%) and food conversion ratio (8·3%) was also shown over the entire 21-d feeding period. 3. The addition of CLI (15 g/kg) to an AF-containing diet significantly reduced the deleterious effects of AF on food consumption and body weight gain. Food conversion ratio was also slightly improved by adding CLI (15 g/kg) to AF-containing diets. Food consumption, body weight gain and food conversion ratio values were rendered numerically intermediate between AF and control groups by the addition of CLI (25 g/kg) to the AF-containing diet. 4. The addition of CLI (both 15 and 25 g/kg) to the AF-free diet did not produce any significant changes compared with the controls, except for decreased total food consumption in the CLI (25 g/kg)-alone group. 5. These results suggest that CLI (15 g/kg) addition effectively diminished the detrimental effects of AF on the values investigated. Also, the lower dietary concentration of CLI (15 g/kg) was more effective than the greater concentration against the adverse effects of AF on the variables investigated in this study.