Rates of respiration and growth were measured for larvae of the spider crab H. araneus reared in the laboratory from hatching to metamorphosis. The moulting cycle was simultaneously monitored. In both zoeal instars individual respiration rate (R) increased as a linear function of time (t) of development, whereas growth, measured as dry weight (W), carbon (C), nitrogen (N), hydrogen (H), and energy content (E, calculated from C) followed a power function of t. Weight-specific respiration rate (QO sub(2)) was in all instars maximum in early postmoult, and minimum in intermoult and early premoult. Zoea II and megalopa instars showed another conspicuous QO sub(2) increase during late premoult. Respiration (both R and QO sub(2)) and growth of the megalopa could be described by non-linear (quadratic) functions of t. R and QO sub(2) during this larval stage were not correlated with W, but were controlled by events of the moulting cycle: R followed a similar pattern to QO sub(2) (minimum values in intermoult), whereas biomass of the megalopa changed conversely, with a maximum in intermoult and early premoult.