The metabolic pathway of cholesterol degradation by bacteria has not been completely established. Several possible intermediates have not been identified and many pathway delineations have not involved the use of the cholesterol molecule per se and just one bacterial species. The bacterial degradation of cholesterol by Pseudomonas sp. NCIB has been studied. Major biotransformation products included cholest-5-en-3-one, cholest-4-en-3-one, 26-hydroxycholest-4-en-3-one, androsta-1, 4-dien-3-17-dione, cholest-4-en-3-one-26-oic acid, chol-4-en-3-one-24-oic acid, pregn-4-en-3-one-20-carboxylic acid, and pregna-1, 4-dien-3-one-20-carboxylic acid. Studies with selected intermediates have enabled the elucidation of a comprehensive pathway of cholesterol degradation by bacteria.