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The chemlcal composihon was analyzed of faecal pellets produced by copepods from Bedford Basin (Nova Scotia, Canada), mainly Pseudocalanus spp. and Temora longicornis, fed dfferent concentrations of the diatom Thalassiosira weissflogii. The feeding response of copepods to day-to-day changes in food concentration involved adjustments of ingestion rate in < 24 h; die1 differences in ingestion rate were found In copepods acclimated to high food concentration but not in those acclimated to low food concentration. Carbon and nitrogen content of faecal pellets (percentage of dry weight) was independent of food concentration, acclimation period to a given food concentration, and ingestion rates. Mean pellet composition was 25 % C and 3 % N; a higher C:N ratio in faecal pellets (7 to 9) as compared with that of the food (5.5) suggested that N was assimilated more efficiently than C. These results suggest that single values of the chemical composition of pellets might be used to estimate vertical flux of carbon and nitrogen via zooplankton faecal pellets. However, a comparison with literature data suggests that differences in carbon and nitrogen content of copepod faecal pellets might result from differences in food quality.