The biological activities of whey proteins on rats treated with 5-fluorouracil were investigated. Histopathological examination of the liver tissue sections obtained from animals that were treated with 5-fluorouracil following administration of whey proteins, showed marked improvement, with mild congested central veins and mild cloudy. Concurrent treatment with 5-fluorouracil and whey proteins caused significant ameliorative changes, where hepatic tissue sections displayed almost normal histology with only mild congestion and dilated central veins. Pronounced improvement in renal tissue was observed in obtained tissue sections from animals treated with 5-fluorouracil following administration of whey protein. No significant alterations were noticed between all treated groups in urea and creatinine concentrations. Whey proteins had no effects on serum iron concentration.