Cassava (Manihot esculenta Crantz) is a cyanide-containing root crop used by many indigenous groups in Amazonia. Despite the availability of low-cyanogenic potential (CNP) cassava, the Tukanoans of the Colombian Amazon region and many other indigenous groups in lowland Amazonia cultivate primarily high-CNP cassava as their staple crop. Based on the assumption that the Tukanoan preference for high-CNP cultivars is due, in part, to the ability of these cultivars to consistently produce higher yields, we tested the null hypothesis that low-CNP cassava has yields that are greater than or equal to the yields of high-CNP cultivars in Tukanoan gardens. To do so we compared the yields of low- and high-CNP cassava in 10 Tukanoan gardens and in one control garden. We reject the null hypothesis: high-CNP cultivars yielded more than low-CNP cultivars in both traditional Tukanoan Indian gardens and a control garden. Although there are several possible explanations for the differences in yields, the most plausible inference is that the high-CNP plants are more likely to be disease and/or insect resistant.