A clear association between seasonal outbreaks of a paralytic disease called konzo and toxic effects from consumption of insufficiently processed bitter cassava roots has been demonstrated in Bandundu region, Zaire. A community-based survey of 6764 inhabitants identified 110 live and 24 dead konzo-affected persons with a history of isolated non-progressive spastic paraparesis of abrupt onset. The start of these annual outbreaks of konzo in 1974 coincided with the completion of a new tarmac road to the capital, which facilitated the transport of cassava and made it the main cash crop. The extensive cassava sales encouraged the consumption by the peasant families of roots that had not been adequately processed; frequent acute cyanide intoxications resulted when the naturally occurring cyanogens in the roots were eaten. The disease mainly appeared in the dry season when there was high consumption of insufficiently processed cassava and the diet lacked supplementary foods with sulfur-containing amino acids which promote cyanide detoxification. These results, which confirm the earlier findings in East Africa, show that, owing to the high cyanide and low sulfur dietary intake, there is an increased risk of konzo outbreaks in cassava-growing areas during periods of adverse agro-economic changes.