Hatchery-reared brown trout, Salmo truttu, (F.L., 16-27 cm) were stocked into the Afon Clettwr, Afon Western Cleddau and Afon Dysynni, Wales. The effects of (a) retaining fish caged in the river for 24 h before release, and (b) a period of acclimation to flowing water (up to 0.24 m S-I) in tanks prior to stocking were investigated. Data on percentage recapture and post-stocking movements were obtained from trapping, electrofishing and tag returns. In-stream acclimation resulted in a higher percentage recapture and a more limited dispersion of the fish stocked under low river flow conditions, but had no effect on trout stocked into a river where higher water velocities were experienced. Acclimation, in tanks, to a flow of 0.1 m s-I for 14 days led to higher percentage recaptures, whereas acclimation for only 2 days resulted in fewer returns than for unacclimated fish. No differences in fish distribution within the rivers could be attributed to these acclimation procedures.