The effect of the addition method of an inducer (o-phthalate) for the enhancement of 4,5-dihydroxyphthalate (DHP) production was examined using Pseudomonas testosteroni. The reduction of the lag phase seen when inducer was added in the first 10 h of growth culture did not affect the maximum production rate of DHP. The optimal inducer concentration was about 2 g dm(-3) and the rate of DHP production was about four times higher that achieved in the absence of inducer. The fed-batch production of DHP was also carried out and 8 g dm(-3) of DHP was obtained.