Experimental studies with both synthetic and real domestic wastewater showed that poly-3-hydroxy-butyrate (3HB) and poly-3-hydroxy-valerate (3HV) formed in direct proportion to the acetate/propionate (Ace/Pro) ratio of the influent wastewater during Enhanced Biological Phosphorus Removal (EBPR). Acetic acid resulted in higher anaerobic phosphorus (P) release, polyhydroxyalkanoate (PHA) yield, 3HB content, and glycogen (CH) degradation. Linear regression showed that anaerobic P release (Prel) and CH degradation (CHdeg) were both a function of Ace-->3HB, but not of Pro-->3HV. Aerobic P uptake (Pup) correlated best with preceding Prel, rather than PHA (but note Prel correlated with Ace-->3HB). Aerobic CH formation (CHform) correlated best with CHdeg and 3HB. The results imply the acetate/propionate content of influent has a major influence on PHA, CH, and P transformations. Short-term increases in acetic or propionic acid increased Prel, but were always offset by corresponding changes in Pup to yield the same net P removal as the control reactor. Thus net P removal, and EBPR process performance, was probably a function of the population selected (i.e. XPAO fraction) during long-term cultivation.