Four diets were prepared to contain 31.12% of either corn (diet 1) or processed cassava peel. The peel was sun-dried, oven-dried or fermented, constituting diets 2-4, respectively. They were fed to weanling giant rats in a 42-day trial. Hydrocyanic acid (HCN) contents of the rations were 0, 130.2, 595.2 and 42.16 ppm, respectively. Performance was best on diet 1, and poorest on diet 3. Metabolizable energy and N retention were poorer in giant rats fed the cassava peel rations. Serum and urinary thiocyanate values were higher (P < 0.01) in the giant rats fed either diet 2 or 3 than in those fed diet 1 or 4. Cyanide intake was significantly (P < 0.05) correlated with daily weight gain, serum protein, urea, thiocyanate, urinary thiocyanate and N retention values. There were no gross or histological lesions in the tissues in any of the test animals.