During isolation of two biosynthetic types of cyanogenic glycosides fromCarica papaya, weak cyanide tests were obtained from initial fractions. Upon final purification, strongly positive cyanide tests were obtained. Pretreatment of extracts to remove polyphenolics alleviated inhibition of cyanogenesis, which led us to suspect that tannins were inhibitory agents. Qualitative and quantitative measures of inhibition were made using standard cyanogenic glycosides and polyphenolics. Cyanogenesis was inhibited quantitatively when condensed tannins (quebracho, wattle, and chestnut), or hydrolyzable tannin (tannic acid) were added. When tannins were precipitated from the reaction mixture, cyanide tests proceeded optimally. These results stress the need to interpret negative cyanide tests with care and indicate possible ecological synergisms between plant defensive chemicals.