The influence of copper (0-32 muM) and iron (0-108 muM) on growth and astaxanthin production by Phaffia rhodozyma was studied. Copper below 3.2 muM increased the astaxanthin content of the cells (from 220 to 287 mug g(-1)) but at the expense of a slightly decreased growth (from 11.3 to 10.2 mg ml(-1)). In contrast, iron below 1 muM decreased both the growth and astaxanthin content of the cells. Using copper limitation instead of toxic respiratory inhibitors to improve astaxanthin production has obvious advantages from the product quality, environmental and process operation points of view.