A modified yeast cell wall extract changed the excretion balance of aflatoxin-contaminated feed fed to dairy ewes. The amount of aflatoxin B1 and its derivative aflatoxin M1 eliminated in feces increased, whereas aflatoxin M1 in urine tended to decrease. The observed increase in aflatoxin elimination in feces is a direct indication that aflatoxin absorption was impaired and suggests that dietary supplementation with this yeast cell wall extract could protect ruminants against the toxic effects of aflatoxins in feed.