Recent studies on the biodegradation of phthalate esters in natural ecosystems, sewage, and laboratory cultures are reveiwed. There is ample evidence to demonstrate that bacteria are major elements in the biodegradative processes and that in most situations complete oxidation of the aromatic ring occurs; much less is known about the catabolism of the alcoholic moiety, e.g., 2-ethylhexanol. Evidence is presented to support catabolic pathways in pseudomonads and niicrococci that are initiated by successive hydrolyses of the diesters to give the phthalate anion.Thereafter a dioxygenase catalyzes the formation of 4,5-dihydro-4,5-dihydroxyphthalate, which is oxidized by an NAD-dependent dehydrogenase to give 4,5,dihydroxyphthalate. Protocatechuate, formed by decarboxylation of 4,5-dihydroxyphthalate, is the substrate for ring cleavage enzymes.Whereas flurorescent pseudomonads use the (J-ketoadipate pathway, the nonfluorescent strains and nhicrococci examined use a meta-cleavage (4,5-1 route. All the intermediates proposed have been accumulated by enzymes purified from Pseudomonas fluorescens. Isophthalate and terephthalate (anions) are readily used as carbon sources by aerobic bacteria, and preliminary evidence is consistent with catabolic routes for these isomers converging at the ring-cleavage substrate protocatechuate. Some possible effects and interactions of synthetic organic chemicals with the natural microflora, and the influence of other vectors, is discussed in relation to the maintenance of the ca'rbon cycle and environmental pollution.Phthalic acid esters (PAEs) have been synthesized on a massive scale for the last two to three decades, mainly for the formulation of plastics. In 1972 production was in excess of 109 lb/yr (1). A conference, sponsored by the National. Institute of Environmental Health Sciences four years ago, focused attention on the accumulation of phthalic acid esters in the environment, and how this might be potentially disadvantageous for the normal development of many life forms, including man. The papers presented were collectively published (1) and two excellent commentary reviews of the meeting appeared in Science (2) and Chemical and