A species of Pseudomonas previously used to study the degradation of p-fluorophenylacetic acid was used to investigate the degradation of p-fluorobenzoic acid. During growth on the latter substrate all organic fluorine was released into the culture medium as fluoride. Several metabolic intermediates were isolated from the culture medium of resting cells. The major compounds have been identified as 4-fluorocatechol, β-acetylacrylic acid, (+)-4-carboxymethyl-4-fiuorobut-2-enolide, (−)-4-carboxymethyl-but-2-enolide, and β-ketoadipic acid. A small quantity of a compound tentatively identified as β-fiuoroacrylic acid was also isolated. On the basis of these findings, together with respiratory studies on p-fluorobenzoic acid grown cells with various substrates, two metabolic pathways are proposed which involve elimination of fluorine at either of two alternative stages in the breakdown of p-fluorobenzoic acid.