No conclusive evidence was found in tests from 1966 to 1969 in either lentic or lotic environments to support the hypothesis that hatchery-reared rainbow trout (Salmo gairdneri) with a high-stamina index had a higher survival potential than those whose stamina index was low. Physical stamina was measured by determining the length of time each fish could withstand sustained swimming in a specially constructed stamina tunnel. For high-stamina rating, fish swam in the tunnel for 80 min; for low stamina, 1–10 min.In tests of reproducibility of stamina ratings, improved swimming ability of low-stamina fish was demonstrated upon retesting in the tunnel. In 1970, with retested fish, still no evidence was found to indicate higher survival of fish rated as high in stamina. Additional studies are needed to determine if performance of hatchery-reared salmonids in a stamina tunnel is a valid indicator of their survival potential in the wild.