In some kinetic studies with aquatic invertebrates, the bioaccumulation of polyaromatic hydrocarbons (PAHs) has been observed to peak at the beginning of the test. This has been explained by the depletion of PAHs from pore water due to limited desorption during the bioaccumulation test or, alternatively, by the activation of biotransformation mechanisms in the organisms. In the present study, we exposed the aquatic oligochaetes, Lumbriculus variegatus, to creosote oil–contaminated sediments to examine the bioaccumulation of PAHs and to clarify the importance of contaminant depletion and biotransformation for it. The contaminant depletion was studied by replanting test organisms into fresh, nondepleted test sediments at 3-d intervals over 12 d and by comparing the resulting body burdens to those of the organisms that were not replanted. The biotransformation capability of L. variegatus was assessed by following the concentration of 1-hydroxypyrene (1-HP), a phase I metabolite of pyrene, in oligochaete tissue during a 15-d test. We observed that the bioaccumulation of most PAHs indeed peaked at the beginning of the test. The concentrations in the replanted organisms were only 1.5 to 2 times higher than in nonreplanted organisms during the first 9 d of the test and, by day 12, no differences were detected. 1-Hydroxypyrene was detected in oligochaete tissue throughout the exposures, and concentrations decreased over time. However, the proportion of 1-HP to pyrene increased linearly during the test. These results indicated that the depletion of contaminants has only a minor effect on their bioaccumulation in oligochaetes and that the cause for the observed bioaccumulation curve shape is rapid elimination of the contaminants and, possibly to some degree, their metabolites.