Using analyses of individuals, dry weight, RNA, DNA and protein content were measured on the same samples to assess the nutritional status of laboratory-reared larvae and juveniles of Solea solea (L.). During the early life of S. solea, 2 growth periods could be distinguished by dry weight measurements and biochemical composition analysis. After metamorphosis, dry weight, RNA, DNA and protein content per individual increased more slowly than before metamorphosis. RNA, DNA and protein were strongly positively correlated to dry weight of fed larvae. Starvation led to immediate loss of weight and to decrease in RNA and protein content, while DNA amount per individual remained roughly constant. Percentage of protein relative to dry weight was always lower in starved larvae or juveniles than in fed ones. DNA and RNA percentages decreased after metamorphosis, but remained always higher in starved than in fed fish. The RNA:DNA ratio continuously decreased during starvation and could be used to discriminate starving from feeding larvae after a few days. However, the RNA:DNA ratio of fed larvae showed relatively large fluctuations during larval development, and its decrease during starvation was strongly dependent upon the ontogenetic stage. The increase of DNA relative to dry weight was also dependent upon the developmental stage of starved larvae, but was much more stable in fed larvae and juveniles. Percentage of DNA can be used to define critical levels (3 % before metamorphosis, 1.5 % after it) above which larvae are undergoing starvation. The usefulness of the RNA:DNA ratio or DNA percentage as indices of nutritional condition is discussed.