Starch and Sago production from cassava (Manihot esculenta Crantz) roots is an increasingly important agro industry. Casssava is one of many cyanogen containing plants. In the present study the amount of cyanogens present in the waste waters and ground waters collected from the starch/sago processing industries in Salem, the main centre of cassava starch and sago production in India was assessed. Concentration of total cyanogens ranged between 12.9 to 66.6 mg 1−1 (as HCN) in the initial processing stages whereas the final discharge contained 10.4 to 27.4 mg 1−1. Linamarase activity of the waste water samples ranged between 3350 to 3370.6 μmoles 1−1 15 min−1. The ground water sources near cassava starch/sago factories showed much higher cyanogen concentration than the acceptable level. The level of total cyanogen in the samples of ground water ranged between 1.2 mg 1−1 to 1.6 mg 1−1.