Castor bean cake was prepared from castor bean seeds roasted at 140 degrees C for 20 min and found free from ricin by chemical analysis. The cake was incorporated into diets at 0, 10, 15, 20 and 25% levels and fed to ducks for 6 weeks. Diarrhoea, emaciation and death were observed mainly at 20 and 25% levels. Congestion of the internal organs and haemorrhagic enteritis were found at necropsy of dead birds. There were necrosis and depletion of the parenchymal cells of the liver and lymphoid organs. Most of the histopathological changes in birds killed after 5 weeks of feeding were more severe at 10 and 15% levels. These lesions included degeneration of the renal epithelial cells, hepatocytes, bile duct proliferation and lymphocytic depletion in the lymphoid organs. The average daily feed intake and weight gain were reduced while the mortality was increased at the higher levels of castor bean feeding. The toxicity of the meal could be due to either a heat stable or growth inhibiting factor or due to minute residues of ricin.