Genetic marking, the manipulation of allelic frequencies to tag fish stocks, was applied to chum salmon Oncorhynchus keta released in Kennedy Creek, a tributary to Totten Inlet in south Puget Sound, Washington. Our objectives were to conduct a Petersen mark-recapture population census of smolts residing in Totten Inlet and to identify the contribution of marked fish to subsequent spawning runs. Male spawners were selected for expression of the 115 allele of aspartate aminotransferase Aat 1,2 or the 90 allele of 6-phosphogluconate dehydrogenase Pgdh. The respective frequencies were thus increased from about 0.12 and 0.01 among the native fish to about 0.25 and 0.11 among the progeny of selected males. Eggs were incubated in streamside gravel box incubators and 11 × 106hatched fish were released to Kennedy Creek during 1978–1980. Fish from the genetically marked broods made up 15–51% of the chum salmon smolts resident in Totten Inlet each spring, 1978–1980, and Petersen mark-recapture population estimates indicated that the total population size ranged from 2.2 × 106to 4.3 × 106. In 1979–1981, 6–29% of adults returning to Kennedy Creek to spawn were fish from marked broods. This study validated the use of genetic marking as a tool for use in fisheries research and management.