A two-stage culture system was established for the production of astaxanthin from Haematococcus pluvialis. In a first stage green vegetative cells were produced in semicontinuous cultures maintained with daily renewal rates between 10 and 40%. The steady-state cell density decreased with increasing renewal rates. Highest cell productivity, 64 x 10(6) cells l(-1) day(-1) was obtained with a daily renewal rate of 20%. In a second stage the harvested cultures were submitted to high light (240 micromol photon m(-2) s(-1)) under batch conditions for 15 days in order to stimulate the transition to the aplanospore stage and the accumulation of astaxanthin. No decrease in cell density was recorded during the induction period in any of the cultures. Cultures obtained at high renewal rates continued growing during the induction period and no astaxanthin was accumulated until all nitrogen in the media had been consumed. The final concentration of astaxanthin was inversely correlated to the growth rate at which first-stage cultures were maintained. Optimal renewal rate for maximal astaxanthin production depended on the duration of the induction period. After a 12-day induction period the highest astaxanthin production, 5.8 mg l(-1) of semi-continuous culture day -1, was obtained with cultures maintained at a renewal rate of 20%. When the induction period was increased to 15 days maximal astaxanthin productivity, 9.6 mg l(-1) of semi-continuous culture day -1, was obtained from cultures maintained at a renewal rate of 40% despite the much lower astaxanthin concentration achieved in these cultures. Results demonstrate the feasibility of semi-continuous cultivation of H. pluvialis for the two-stage production of astaxanthin.