Three strains of Acinetobacter isolated from activated sludge were examined for their capacities to produce polyphosphate and poly-β-hydroxybutyrate following growth under phosphate, ammonia and sulfate limitation. When growing on complete medium levels of polyphosphate produced by RA3117 were about six times higher than in RA3757 and levels were unchanged when growing on ammonia or sulfate limitation. Strain RA3197 produced polyphosphate only when subjected to sulfate limitation. No strain produced polyphosphate when growing under phosphate limitation. When the three strains were grown in normal medium at 100% oxygen saturation, no strain produced poly-β-hydroxybutyrate. When subjected to phosphate, ammonia or sulfate limitation RA37S7 produced up to 10% PHB as dry weight. Strains RA3117 and RA3197 produced moderate amounts of sudanophilic material only when grown under phosphate limitation, however, only trace levels of PHB were detected. In RA3757 levels of the poly-β-hydroxybutyrate synthesizing enzymes - β-ketothiolase and acetoacetyl-CoA reductase - correlated well with poly-β-hydroxybutyrate production but in strains RA3117 and RA3197 no activity of either of the enzymes was observed.