Larval and early post-larval growth has been investigated in H. araneus L. (Majidae) reared in the laboratory. Growth was measured as dry weight (DW), ash-free dry weight (AFDW), carbon (C), nitrogen (N), hydrogen (H), gross biochemical constituents (protein, lipid, carbohydrate, chitin, ash) and energy (calculated separately from carbon and biochemical composition). During larval development, i.e. from freshly hatched zoea-I to late megalopa, all these criteria of biomass increase by factors ranging between 5 and 14; carbohydrate shows the lowest, chitin the highest increment. There are indications of loss in organic body weight during the latest period preceding metamorphosis to the crab stage. When no food is offered during this time, megalopae lose significantly more biomass than control larvae. This suggests that food is still required, but feeding activity is reduced to a level below maintenance ingestion rate. Following metamorphosis, the juvenile crab accumulates biomass at a far higher absolute rate (expressed as µg/d) than all larval stages.