Response to stress during the spawning period of sockeye salmon (Oncorhynchus nerka) was investigated by measuring cortisol, selected steroids and glucose levels in the plasma of cultured fish under acute confinement conditions. Fish were individually placed in nets and sacrificed to obtain blood samples after each confinement period: 0, 3, 5,15 and 30 min, respectively. In males, acute stress increased cortisol levels in the plasma at 15 min and testosterone, 11-ketotestosterone and glucose levels in the plasma within 3 min. In females, the cortisol level was higher than that in males and did not significantly change at 15 and 30 min. Testosterone levels in females decreased at 15 min in confinement. Progesterone, 17-hydroxyprogesterone and 17,20 β-dihydroxy-4-pregnen-3-one levels did not change with confinement time in females. To know the reproductive stage of the fish used in the stress experiment we collected blood and measured sex steroid hormones in different fish from the same pond one week and one day before the experiment. In these fish, the sex steroids in males and females changed with the pattern of breeding. Cortisol levels were higher in females than in males for one week. This study demonstrates that the cortisol level in females is higher than in males during their spawning period, and that females might be less sensitive to changes in the level of cortisol caused by acute stress than are the males.