A newly isolated solvent-tolerant Pseudomonas putida strain converts (+)-limonene to high concentrations of a single and stable product, perillic acid. The presence of a cosubstrate is necessary for growth and perillic acid production. Glycerol appears to be the most suitable cosubstrate among those tested. An optimal combination of 150 mM limonene and 50 mM glycerol was found. Other factors that improve the extent and/or rate of bioconversion are the use of ammonia or urea as the nitrogen source, control of temperature at 30-34 degrees C and of pH at 7.0, as well as the use of emulsifiers to increase the bioavailability of limonene. Up to 18 mM (3.0 g . l(-1)) perillic acid is produced, a concentration that is not growth inhibitory. The observations that a single product is formed in high concentrations and that it is not further metabolized make this limonene bioconversion of commercial interest.