Candida utilis contains an inducible enzyme, urea amidolyase, which catalyzes the decomposition of urea with formation of carbon dioxide and ammonia. This reaction is accompanied by the cleavage of ATP with liberation of equimolar amounts of ADP and inorganic phosphate, is strictly dependent for activity on divalent (Mg++ or Mn++) and monovalent (K+, Rb+, Cs+, or NH4+) cations, and requires catalytic amounts of bicarbonate. A detailed consideration of these properties is presented for the enzyme purified approximately 150-fold from C. utilis. Urea amidolyase activity is induced in C. utilis by urea and other substances which most likely are enzymatically degraded to urea. Repression of the enzyme occurs when low evels of ammonia are present in the medium. Extracts of other yeasts, such as Candida flareri and Saccharomyces cerevisiae, as well as of the unicellular green algae Chlorella ellipsoidea, Chlorella pyrenoidosa, and Chlamydomonas reinhardtii, also contain urea amidolyase activity when these organisms are grown in media containing urea as the sole source of nitrogen.