The biosynthesis of poly(hydroxyalkanoates) (PHA) by Pseudomonas resinovorans from triglyceride substrates was investigated. Each triglyceride, whether animal fat or vegetable oil, supported cellular growth to relatively high average cell yields (3.3 +/- 0.2 g/l). PHA yields ranged from 1.1 g/l to 2.1 g/l, representing approximately 45% of the bacterial cell dry weight. The repeat-unit composition of the polymers was determined by gas chromatography (GC) and GC/mass spectrometry of the beta-hydroxyalkanoate methyl esters from the hydrolyzed polymers. With the exception of PHA from soybean oil (PHA-soy), each polyester was composed of beta-hydroxyacyl moieties with chain lengths ranging from C-4 to C-14, with C-8 and C-10 being the predominant species. PHA-soy contained an additional fraction (2%) of C-16 monomers. The alkyl side-chains of the PHA contained varying degrees of unsaturation. PHA from coconut oil was composed entirely of saturated sidechains, whereas PHA-soy contained 4.2 mol% olefinic groups in its side-chains. The increase in the degree of side-chain unsaturation caused decreased melting temperatures, enthalpies of fusion, and glass transition temperatures. The molar masses of the polymers were relatively constant and ranged from 6.5 x 10(4) to 10.1 x 10(4) g/mol.