The effect of graded levels of thiamin on the metabolism of linamarin was investigated in rats. It was observed that on a diet deficient in thiamin, a large amount of linamarin was recovered unchanged in the urine, together with significantly more thiocyanate (SCN–) relative to the control. The least amount of thiocyanate (p < 0.05 relative to control) was found in animals receiving the highest amount (twice daily requirement) of thiamin in the diet; but the amount of unmetabolized linamarin was similar to the control. It is suggested that thiamin deficiency may be implicated in the aetiology of tropical ataxic neuropathy (TAN) through the thiocyanate overload in people eating large amounts of cassava and cassava derivatives which contain linamari