The secondary production of the harpacticoid copepod Tachidius discipes Giesbrecht 1881 was estimated during spring 1979. The population was sampled every 3 d. Three generation peaks were observed. These were clearly distinct in the first copepodite stages, but gradually showed more overlap in older stages. Production of copepodites and adults was estimated in 2 ways: (1) Peaks were separated and the forward shifting of peaks in consecutive stages was used to estimate stage durations; (2) the size-frequency method was applied. Both estimates of the production of copepodites and adults are in good agreement: 1.10 g dwt m-2 and 1.02 g dwt m- 2 • Egg production amounts to 0.31 g dwt m- 2 ; naupliar production is roughly estimated at 1.11 g dwt m- 2 . The production efficiency, P/(P+R), of copepodites and adults is 0.36; for the total population it is 0.43. This value corresponds well to the value estimated from culture experiments with this population.