The precursor of the volatile S-compound dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), is produced by marine microalgae, notably by Prymnesiophyceae. The production of DMSP by an axenic isolate of Emiliania huxleyi (Lohm.) Hay et Mohler under different temperature and light conditions was studied as a first step towards understanding the role of DMSP-producing algae in climate regulation. Both light and temperature affected growth rate and cell size in batch cultures, but the concentration of DMSP in the cells was dependent on temperature only: at low temperature DMSP accumulated. This physiological response, assumed to be characteristic of DMSP-producing microalgae in general, is in line with the correlation that has been found between elevated concentrations of the DMS oxidation product MSA in ice core slices corresponding with low sea surface temperatures. Apparently, DMS does not play the role in climate regulation formulated in the CLAW hypothesis that proposes a feedback mechanism in which elevated temperatures lead to an increase in albedo via DMS-derived cloud condensation nuclei. (C) 2002 Elsevier Science B.V. All rights reserved.