This study was conducted to evaluate the protective efficacy of clinoptilolite (CLI, a natural zeolite) in the prevention of toxic effects of aflatoxin (AF). A total of 576 1-day-old Ross broiler chicks were housed in six treatment groups [six replicates of 16 each; control, CLI (15 g kg-1 diet), 50 parts per billion (ppb) AF, 50 ppb AF plus CLI, 100 ppb AF, 100 ppb AF plus CLI] for 42 days. Compared to controls, 100 ppb AF treatment significantly decreased body weight gains of chicks. The addition of CLI to the 100 ppb AF-containing diet moderately reduced the adverse effects of AF on performances of chicks. The chicks consuming 50 ppb AF-containing diet showed no significant differences on investigated parameters compared to controls. Also, the single addition of CLI to the AF-free diet had no adverse effects in birds. These results suggest that CLI can be beneficial in broilers for protection of AF toxicity at the level above. (C) 2000 Harcourt Publishers Ltd.