The respiratory metabolism of first stage Macrobrachium olfersii (Wiegmann) zoeae was measured at 12 hr intervals with Cartesian diver microrespirometers throughout the 120 hr period from eclosion to first ecdysis. Weight-specific oxygen consumption rates, although slightly higher immediately after hatching, remained constant and did not differ significantly during the first moulting cycle. Larval dry weight decreased from 21.8 to 18.9 @tg during this period. There was no evidence of a diurnal metabolic pattern. The nioulting cycle was subdivided according to morphological characteristics, based on the degree of cytoplasmic homogeneity, epidermal retraction, and stage of setal development in the telson. Larval metab olism is suggested to be uniform throughout the eclosionâ€"first ecdysis period, in spite of a distinct and divisible nioulting cycle.