Results from a 28-day adult reproductive bioassay using the aquatic oligochaete Tubifex tubifex (Müller, 1774) are compared with life table statistics obtained from a 6-month experiment on cohorts of the same species. This was done by simultaneously performing the two tests on copper spiked sediments. Five concentrations and a control were tested. The 28-day bioassay was performed 3 times in succession. Several endpoints were considered for each test and LOEC, IC10 and IC50 were calculated. IC50 estimates for the number of young produced in the 28-day bioassay range from 81 to 107 mg/kg; IC50 estimates for different endpoints of the cohort experiment ranged from 88 to 106 mg/kg. The 28-day bioassay showed essentially the same sensitivity as the cohort experiment to copper. This suggests that the 28-day reproductive bioassay does provide information that is relevant in assessing long-term toxic effects at the population level.