The effects of incident light intensity (15-218 W m-2) on growth and biochemical composition (protein, lipid, chlorophyll and fatty acid profiles) of the marine microalgae Isochrysis galbana Parke and Tetraselmis sp. were examined under controlled laboratory conditions in batch cultures. The maximum specific growth rates reached for 1. galbana Parke and Tetraselmis sp. were 0.032 h-1 and 0.059 h-1, respectively. Growth became light saturated between 80 and 100 W M-2 for both species. The different biochemical compound productivity values were fited to the same empirical equation. Tetraselmis sp. yielded the highest protein and chlorophyll productivities, while lipid productivity was highest in Isochrysis galbana. The greater eicosapentaenoic acid (EPA) concentrations and productivity were found in Isochrysis galbana Parke.