Exuvial losses in relation to late premoult matter and energy, and in relation to growth achieved during each instar, were studied in laboratory-reared larvae and early juveniles of the decapod H. araneus (L.). Changes of composition during development were measured in the complete body and in the exuvia from hatching through the second crab stage. Rates of exuvial loss increased during development in all parameters measured. They were generally highest in inorganic carbon and lowest in N. six to 7% of late premolte energy was lost by moulting zoeae, i.e. 9 to 13% of the energy produced during these stages. The megalopa lost 13%, and juveniles 19 to 20% of their LPRM energy ( similar to 29 to 41% of growth). During complete larval development of H. araneus a total of 18% of produced energy was lost at ecdysis. The same amount had been reported in the literature for larval development of 3 other decapod species.