Phenyldecane supported growth and lipid accumulation of Rhodococcus opacus PD630 during cultivation under nitrogen-limiting conditions. The results of this study suggested that the hydrocarbon phenyldecane was degraded by monoterminal oxidation, followed by beta-oxidation of the alkyl side-chain to phenylacetic acid, and by an additional degradative route for the oxidation of the latter to intermediates of the central metabolism. alpha-Oxidation of phenyldecanoic acid also occurred to some extent. Phenyldecanoic acid, the monoterminal oxidation product, was also utilized for the biosynthesis of a novel wax ester and novel triacylglycerols. The formation of the wax ester phenyldecylphenyldecanoate probably resulted from the condensation of phenyldecanoic acid and phenyldecanol, which were produced as metabolites during the catabolism of phenyldecane. Two types of triacylglycerol were detected in phenyldecane-grown cells of strain PD630. Triacylglycerols containing only odd- and even-numbered aliphatic fatty acids, as well as triacylglycerols in which one fatty acid was replaced by a phenyldecanoic acid residue, occurred. Other phenyl intermediates, such as phenylacetic acid, phenylpropionic acid, 4-hydroxyphenylpropionic acid, protocatechuate and homogentisic acid, were excreted into the medium during cultivation on phenyldecane. On the basis of the results obtained, pathways for the catabolism and assimilation of phenyldecane by R. opacus PD630 are discussed.