Studies were made to evaluate the content of hydrocyanic acid in the core of cassava roots. Seven varieties of the sweet cassava group and two varieties of the bitter type were analysed in order to evaluate the differences between plants, size of roots and age of plants. The results obtained point out large differences between the two groups. Among the edible varieties, Vassourinha, Tatu and Branco do Pomar presented a high amount of hydrocyanic acid. Nevertheless they con be safely used as human food, after cooking. Since no statistical differences were found between plants, size of roots and age, the sampling technique will be much easier in the future.