Temperature and pH had only a slight effect on the astaxanthin content of a Phaffia rhodozyma mutant, but influenced the maximum specific growth rate and cell yield profoundly. The optimum conditions for astaxanthin production were 22 degrees C at pH 5.0 with a low concentration of carbon source. Astaxanthin production was growth-associated, and the volumetric astaxanthin concentration gradually decreased after depletion of the carbon source. The biomass concentration decreased rapidly during the stationary growth phase with a concomitant increase in the cellular content of astaxanthin. Sucrose hydrolysis exceeded the assimilation rates of D-glucose and D-fructose and these sugars accumulated during batch cultivation. D-Glucose initially delayed D-fructose uptake, but D-fructose utilization commenced before glucose depletion. In continuous culture, the highest astaxanthin content was obtained at the lowest dilution rate of 0.043 h(-1). The cell yield reached a maximum of 0.48 g cells g(-1) glucose utilized between dilution rates of 0.05 h(-1) and 0.07 h(-1) and decreased markedly at higher dilution rates.