Detoxification of commercial aflatoxin B1 (AFB1) contaminated feed by means of 1N aqueous citric acid was confirmed by the AFLATEST? immunoaffinity column method (IAC), high performance liquid chromatography (HPLC), Ames test (Salmonella-microsomal screening system), and the 1-day duckling assay. IAC and HPLC determinations showed that AFB1 at an initial concentration of 110 ng/g was partially detoxified (86%) by the acidic treatment. Results of the Ames test indicated that the mutagenic activity of treated AFB1 was greatly reduced (or inactivated) compared with that of untreated controls based on his- ¡ú his+ reversions in the Salmonella TA100 strain. The toxicology and pathology studies showed that toxicity of AFB1 was minimized by acidic treatment. The results indicated that aqueous citric acid exhibits detoxifying activity in AFB1-contaminated feeds and protects animals from chronic aflatoxin toxicity.