Lamina samples of four cassava (Manihot esculenta Crantz) clones - TMS/GP/B 4107, RP/B 5028, U 42046 and W 4488 - infected by the African cassava mosaic disease (ACMD) were assessed for total cyanide, 3-5 months after field propagation, using an enzymatic assay method. Cyanide content of leaves of varying ages from paired plants (with and without ACMD symptoms) and plants grouped into classes of symptom severity were compared. Contents varied considerably (ca 500-3500 mg kg-1 fresh wt), and differences between means were significant (P < 0.01). Depending on the level of infection and other factors, HCN values increased, reduced or remained unchanged. The variations are explained on the basis of known effects of plant viruses on host carbohydrate and nitrogen metabolism.