A coho salmon stock assessment program was initiated in 1991 to assess the status of Kenai River wild stocks. As part of the program, this project deals with estimating the contribution of Kenai River stocks to commercial marine harvests in Upper Cook Inlet. To identify Kenai River adults in the commercial harvest, juvenile fish were captured in the Kenai River drainage and marked with a coded, microwire tag and an adipose finclip. The proportion of marked Kenai River adults in the commercial harvest will be expanded to estimate the contribution of Kenai River adult coho salmon to the commercial fishery. Rearing fingerling were captured with modified fyke traps in the fall of 1992 at the outlets of Kenai and Skilak lakes. Smolt were captured during the spring of 1993 at weirs in Hidden Creek and the Moose River, both tributaries of the Kenai River. An estimated 141,925 coho salmon were released with one of 33 unique microwire tags between 13 August and 28 June 1993. Short-term tag retention exceeded 98% at all four marking locations in the drainage. Short-term survival rates exceeded 99%. Tag retention and survival rates were higher for marked fingerling than for smolt. Fingerling captured at the outlets of Skilak and Kenai lakes in the fall of 1992 consisted primarily of age-0 and age-1 coho salmon. The percentage of age-1 fish in the trap catch declined between 13 August and 14 October. The mean fork length of age-1 fish sampled weekly ranged from 86 millimeters to 125 millimeters. Smolt captured in the spring of 1993 were primarily age 2 at both the Moose River (88.7%) and Hidden Creek (65.8%). The mean length of age-2 fish emigrating from the Moose River (125 millimeters) was smaller than those emigrating from Hidden Creek (136 millimeters). Coho salmon marked as fingerling in 1992 were recaptured as they emigrated from the Moose River and Hidden Creek in 1993. This indicates that some individuals disperse from their natal area during freshwater residency and that localized groups of fish may be aggregates of fish from a variety of natal areas. Coho salmon marked at both tributaries in 1993 were recaptured by inclined-plane traps located in the mainstem Kenai River (river kilometer 31.0) downstream from the tributaries. A comparison of length distributions of smolt measured at the tributaries with those of marked fish recaptured in the traps suggests that the inclined-plane traps are size selective toward smaller coho salmon. An estimated 34% of the 1,982 coho salmon captured by the inclined-plane traps were marked. For designing a commercial catch sampling program for the 1994 harvest, this is a maximum expected marked proportion of the Kenai River adult return. Size selectivity of the inclined-plane traps and past performance of this estimate suggest that the estimated proportion of marked coho in the adult return will be lower than 34%.