Sixteen Pseudomonas aeruginosa strains, including patent strain NRRL B-18602, three recent isolates from composted materials amended with ricinoleic acid, and 12 randomly selected from the holdings of the ARS Culture Collection, were examined for their fatty acid converting abilities. The study examined the bioconversion of oleic acid to 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) and ricinoleic acid to 7,10,12-trihydroxy-8(E)-octadecenoic acid (TOD). A new DOD-like compound from linoleic acid was observed. All strains except NRRL B-247 exhibited varying levels of DOD production. NRRL B-1000, NRRL B-18602 and NRRL B-23258 with yields up to 84% were among the best DOD producers. TOD production generally paralleled DOD production at a relatively lower yield of up to 15%. Strains NRRL B-1000 and NRRL B-23260 were the best TOD producers. A DOD-like product in low yields was obtained from linoleic acid. The fatty acid bioconversion capability was related neither to growth rate nor to variation in the greenish pigmentation of the strains. Production of significant quantities of DOD and TOD from oleic and ricinoleic acids, respectively, appeared to be a characteristic trait of P. aeruginosa strains. A number of highly effective strains for DOD production were identified.