The bacteria Pseudomonas oleovorans, P. resinovorans, P. putida, and P. citronellolis were evaluated for their ability to grow and produce poly(hydroxyalkanoates) (PHA) using tallow free fatty acids and tallow triglyceride as carbon substrates. Tallow free fatty acids supported cell growth and PHA production for all four organisms, yielding PHA contents of 18%, 15%, 19% and 3% of their cell dry weights for P. oleovorans, P. resinovorans, P. putida, and P. citronellolis respectively. Only P. resinovorans, however, was able to grow and produce PHA polymer. with cells attaining a PHA content of 15% of their cell dry weight, using unhydrolyzed tallow as the substrate, Extracts from 46-h cultures of P. resinovorans were found to have a higher esterase activity (12.80 units mu l(-1)min(-1)) compared to the activities found for cultures of P. oleovorans, P. citronellolis, and P. putida (< 0.03 units mu l(-1)min(-1)). Polymer repeat-unit compositions were determined by GC analysis of the beta-hydroxymethyl esters of hydrolyzed PHA, and ranged in carbon-chain lengths from C-4 to C-14, with some mono-unsaturation in the C-12 and C-14 side-chains. PHA compositions were similar for the polymers obtained from all four organisms, with repeat units of chain lengths C-8 and C-10 predominating.