The distribution of benthic invertebrates was studied under different flow regimes in an unregulated West Norwegian river. A total of 150 quantitative benthic samples was taken from fixed transects at three different stations in the river. Hydrophysical characteristics were recorded at each sampling spot. The depth and flow preferences of the different species varied. According to the distribution, two of the species, the caddisflies Polycentropus fiavomaculatus and Oxyethira spp., were closely associated with shallow, slow-flowing areas, differing significantly from nearly all the other species tested. Rhyacophila nubila, Baetis rhoduni and Glossosoma intermedia were all classified as rheophilic, not differing significantly in preferences of water velocity and depth. Diura nanseni was most abundant in water velocities above 30cm s-' . This species preferred shallow areas, in contrast with Leuctra hippopus and G . intermedia. Three of the species, Amphinemura sulcicollis, A . borealis and L. hippopus were classified as indifferent with respect to water velocities. Gaussian logit and linear logit regression showed that only one of the species tested, A . borealis, had a significant response curve to the depth of the water column. The density of this species decreased sigmoidally with an increase in depth. D. nanseni was the only species showing a significant response to the water velocity.