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Zooplankton samples were collected from 0 to 50 m depth at 2 stations in Jones Sound and 1 in Baffin Bay in August and September of 1983. Levels of chlorophyll and phaeopigment were measured in several stages of Calanus hyperboreus and Calanus glacialis at 4 h intervals, to examine diurnal feeding behavior in copepods which do not vertically migrate on a daily basis. All stages examined for each of the 2 species showed diurnal variations in feeding activity. In addition, different stages and species always started to feed synchronously, although timing of onset of evening feeding was different at each of the 3 stations. On each occasion feeding started when incident light intensity decreased to < 4 W m-2. Cessation of feeding in the morning, however, was not linked to a particular intensity of incident light and may be controlled by satiation of appetite. Levels of 3 digestive enzymes -protease, laminarinase, and amylase -were measured in 2 stages of C. hyperboreus and C. glacialis at 4 h intervals over a 48 h time series at the second of the Jones Sound stations. There were no rhythmic changes in amounts of enzymes in any of the stages. Maximum levels of gut pigment within any 1 stage were not necessarily correlated with ambient chlorophyll concentrations, which varied by a factor of 4 among stations.