The euphausiid fauna of the Rockall Trough has been sampled in time series at approximately two-monthly intervals between 1973 and 1976 between surface and depths greater than 2000 m. Length/frequency histograms have modes that are coherent for periods of at least 4 to 6 mo, indicating that populations are being sampled. Rates of growth were determined for six species. Epipelagic species have winter checks to the growth rates, but such checks are absent in the growth of Thysanopoda acutifrons, Nematobranchion boopis and Stylocheiron maximum. Ratios of annual production: biomass were determined and are all within the previously determined range of values for epipelagic and coastal populations. Lack of a winter check to the growth rate in deep-living species enables these potentially to have overall rates of growth comparable to those of temperate, epipelagic, shelf and coastal species.