A mutant of Candida tropicalis was used to convert n-alkanes to the corresponding alpha,omega-dicarboxylic acids (DC). Effects of medium pH on dioic acid productions were studied in batch fermentations in which growth and conversion were separated into a growth and a conversion phase. A pH control strategy for the high-level production of alpha,omega-tridecanedioic acid has been proposed and optimized, i.e. programmed incremental pH increase from pH 7.2 to 8.10 during DC production stage, the dioic acid concentration reached 153 g/l after 120 h transformation and demonstrated a 22% increase in production compared to that obtained with an optimized constant pH value. Using the optimal strategy for n-dodecane and n-tetradecane fermentation, the corresponding dioic acid concentrations reached 166 and 138 g/l, respectively. The influences of the strategy on cytochrome P450 monooxygenase activity of the cells were also examined; the maximum activity of the enzyme can be maintained for a longer period of time during the conversion phase using by this optimal strategy. (C) 2003 Published by Elsevier Inc.