The ability of benthic polychaetes to move as adults and juveniles was examined using flume experiments. The main question asked was whether post-settlement movement is a passive process predictable from the hydrodynamic characteristics of the environment and the individual, or whether active behavior is involved. In one set of experiments, the percent of individuals moving during a six-hour period in low-food conditions was compared among five species of intertidal polychaetes. Flow speed was set at a velocity that did not cause sediment erosion but did cause bedload transport of anesthetized individuals. Species varied significantly in percent of movement, with Laeonereis culveri, Nereis succinea and Lumbrineris tenuis displaying negligible movement, Polydora cornuta having small but consistent movement, and Streblospio benedicti displaying the most movement (27% of individuals leaving original sediments in 6 h). Movement was not related to body size or mode of development, but showed a correlation with depth/feeding preferences: subsurface-feeders moved less than interface-feeders. Experiments with P. cornuta and S. benedicti that were extended to 18 hours indicated that post-settlement movement continued but the rate of movement during hours 6 -18 was approximately half that during the first 6 hours. Experiments looking at the effects of experimental conditions on post-settlement movement in S. benedicti found that darkness had no effect, but that adding food, holding adults in still-water culture for 2.5 months, or growing larvae to adults in still-water cultures all significantly decreased movement. Overall, the results indicated an active component to post-settlement movement.