Chlamydomonas acidophila growing autotrophically with continuous PAR light (160 mu E m(-2) s(-1)) and 30 degrees C may accumulate carotenoids which increase in response to abiotic stress, like high light intensity, UV-A radiation and temperature fluctuation. At PAR light of 240 mu E m(-2) s(-1) the alga contains, after 20 days of growth, 57.5 +/- 1.6 mg l(-1) of total carotenoids, which does not significantly change by an irradiance of 1000 LE m(-2) s(-1). Lutein (20 +/- 0.5 mg l(-1)) and beta-carotene (8.3 +/- 0.2 mg l(-1)) production were particularly high in C. acidophila, while zeaxanthin (0.2 +/- 0.1 mg l(-1)) was low. Enhanced production of lutein and beta-carotene were observed in the alga grown under standard conditions, but either supplemented with moderate UV-A radiation (10 LE m(-2) s(-1)), or heated at 40 degrees C. The presence of Fe3+ in the culture medium, in a range between 5 and 35 mM, significantly decreased the C acidophila viability and the intracellular carotenoids content. However Cu2+, at 1-5 mM, appears to increase the synthesis of beta-carotene. The alga can grow under mixotrophic conditions, with glucose, 10 mM, as carbon source, but any of such conditions improved the intracellular content of carotenoids. (C) 2008 Elsevier Ltd. All rights reserved.