A survey has been made of the occurrence and distribution of three enzymes which metabolize cyanide in a variety of higher plants including both cyanogenic and non-cyanogenic species. The enzymes investigated were beta-cyanoalanine synthase, rhodanese and formamide hydrolyase. beta-Cyanoalanine synthase was found to be present in every higher plant tested whereas rhodanese was found to occur far less commonly in plants. Formamide hydrolyase activity was not detected in any of the higher plants tested.In addition, quantitative analyses have been made of the potential hydrogen cyanide content of each plant investigated. A general trend was apparent between the hydrogen cyanide potential and cyanide metabolizing activity, in that the higher the hydrogen cyanide potential, in general, the higher the cyanide metabolizing activity.