Citrullus colocynthis seed was fed at 2% and 10% of the basal diet to 7-d-old Bovans-type chicks for 6 w. Average body weights and efficiency of feed utilization were markedly depressed in the chicks on 10% Citrullus feed, and the serum activities of LDH, AST and CK and concentrations of total lipid and zinc were significantly increased. The concentration of serum total iron binding capacity was particularly reduced in chicks on 2% Citrullus feed. The concentrations of other serum and blood constituents and of hepatic copper, manganese and zinc were not significantly changes. Lesions seen in the intestines, livers, kidneys and other tissues were fully reversed 4 w after removal from the experimental diet.