The microalga Haematococcus pluvialis was cultured with NaNO3 from 0 to 1 g l(-1) and optimal growth was obtained at 0.15 g l(-1). Sodium acetate and malonate (from 0 to 2% w/v) enhanced the accumulation of astaxanthin three and five times higher, respectively, than in autotrophic control cultures. However, high concentration of those compounds strongly inhibited growth. The ratio chlorophyll a/total carotenoids was a good indicator of the extent of nitrogen deficiency in the cells.