1. Pseudomonas sp. N.C.I.B. 8858 grew well on Dand L-1-aminopropan-2-ol and on aminoacetone. 2. Cell-free extracts possessed high activities of inducibly formed L1-aminopropan-2-ol-NAD+ oxidoreductase, amino alcohol-ATP phosphotransferase, DL-1-aminopropan-2-ol 0-phosphate phospho-lyase and aldehyde-NAD+ oxidoreductase, but no 1-aminopropan-2-ol racemase or D-I-aminopropan-2-ol-NAD+ oxidoreductase. 3. The amino alcohol kinase (activated by ADP) was non-stereospecific towards 1-aminopropan-2-ol and was one-third as active with ethanolamine. The phospho-lyase was active with Land D-1-aminopropan-2-ol 0-phosphate, but ethanolamine 0-phosphate was only one-tenth as active as its higher homologues. The purified aldehyde dehydrogenase was active with propionaldehyde, acetaldehyde and also with methylglyoxal. The previously observed 2-oxo aldehyde dehydrogenase activity was considered to be due to the broadly specific aldehyde dehydrogenase. 4. Mutants of Pseudomonas sp. N.C.I.B. 8858 deficient in 1-aminopropan-2-ol kinase, 1-aminopropan-2-ol 0-phosphate phospho-lyase, aldehyde dehydrogenase or an enzyme involved in propionate metabolism were incapable of growth on aminoacetone or 1-aminopropan-2-ol as carbon source, although all except the kinaseor phospho-lyasedeficient mutants could use these compounds and ethanolamine as nitrogen sources. The aldehyde dehydrogenase-deficient mutants produced copious amounts of propionaldehyde and acetaldehyde during growth on the corresponding amino alcohols. 5. The path of aminoacetone metabolism in Pseudomonas sp. N.C.I.B. 8858 was concluded to involve L-1-aminopropan-2-ol, the 0-phosphate ester of this compound, propionaldehyde and propionate as obligatory intermediates. D-1-Aminopropan-2-ol was metabolized by the same route as the L-isomer, gratuitously inducing formation of the stereospecific L-1aminopropan-2-ol dehydrogenase. 6. Extracts of the pseudomonad grown with ethanolamine as the nitrogen source were devoid of 1-aminopropan-2-ol dehydrogenase, the kinase and the phospho-lyase, but exhibited cobamide coenzyme-dependent deaminase activity. Mutants deficient in kinase or phospho-lyase (deaminating) grew well on ethanolamine as the nitrogen source. Ethanolamine deaminase was inactive with, but inhibited by, 1-aminopropan-2-ol.