Several biochemical and physiological characteristics of stage V and female adult Calanus hyperboreus from two different depth ranges (0–50 m and 200–500 m) were compared at a time near the peak of the summer pelagic algal bloom in Jones Sound, and again one month later, when the near surface chlorophyll levels were low and most copepods had migrated to their overwintering dephts. For a given stage deep water animals were larger and had higher total lipid levels than did surface animals. Feeding activities, as evidenced by gut pigment contents, may be lower in animals at depth, although potential digestive activities, as expressed in the levels of three digestive enzymes, were not very different either in different stages or at different depths. Respiration rates in animals that had migrated down for the winter were not much lower than in those at the surface although energetic considerations suggest that they may decrease later. Ammonia excretion rates however, changed dramatically. Surface, feeding animals had the highest rates and deep water animals in September had undetectably (<1 ng="" atom="" ammonia="" nitrogen="">^-1 · day^-1) low rates.