The susceptibility of cytochrome oxidases to cyanide means that cyanide is toxic to living cells and cyanide pollution causes great damage to microbial and other ecosystems. Cyanide pollution comes from both industrial wastes and a number of plants, many of agricultural importance, which are cyanogenic and release cyanide into the soil. Despite some understanding of the pathway of cyanide assimilation by aerobic microorganisms, there is little known about cyanide assimilation by anaerobic microorganisms. The author discusses cyanide production, utilization, degradation, and resistance by microorganisms. He concludes that among the most primitive organisms were some that could metabolize cyanide, perhaps in conjunction with other carbon and nitrogen sources. 199 references, 4 figures, 2 tables.