Abstract Two nineteen day rat gestation/metabolic studies were carried out with thirty female rats to investigate the influence of fresh and dried cassava containing 173 parts/10 6 and 92 parts/10 6 HCN respectively on placental thiocyanate transfer, metabolic changes in maternal and foetal tissues and their gestational performance. The cassava diets caused marked changes in the weight gain and thiocyanate concentration of the urine and serum of the gestating rats. Amniotic fluid thiocyanate was significantly increased by the fresh cassava diets ( P <0.01), but foetal thiocyanate was not significantly different between treatments ( P >0.05). Rhodanese activity and fresh weights of maternal and foetal tissues were also not significantly affected by the cassava diets ( P >0.05).