Catch-and-release fishing regulations are widely used by fishery resource managers to maintain both the quantity and quality of sport fish populations. We evaluated blood chemistry disturbances in wild brook trout Salvelinus fontinalis, brown trout Salmo trutta, cutthroat trout Oncorhynchus clarkii, and Arctic grayling Thymallus arcticus that had been hooked and played for 1-5 min in waters of the intermountain western United States. A hatchery stock of brown trout was included for comparison. To assess time needed for recovery, additional test groups were played for 5 min and then released into net-pens, where they were held for up to 72 h. The osmoregulatory and metabolic disturbances associated with catch-and-release fishing under the conditions we tested were minimal and judged to be well within normal physiological tolerance limits. In fish that were held for recovery, the blood chemistry alterations that did occur appeared to be related to stress from confinement in the net-pens. Our results confirm the results of previous studies, showing that prerelease air exposure and handling cause more physiological stress than does either hooking per se or playing time. Fishery managers must be aware of the differences in the perceptions, attitudes, and values of different societal groups, some of which feel that catch-and-release fishing should be banned because it is cruel to the animals. On the basis of brain anatomy, it seems highly unlikely that fish experience pain in the same manner as humans experience it, because fish lack a neocortex, the brain structure that enables the sensation of pain in higher vertebrates. However, independent of the neurobiological argument, our results indicate that under conditions similar to those tested, fish subjected to catch and release are neither suffering nor particularly stressed. Improved education programs about the relatively benign physiological effects of catch-and-release fishing as a fishery management practice would be beneficial to anglers and the nonfishing public alike.