The passage of chinook salmon Oncorhynchus tshawytscha in the Kenai River was estimated using side-looking split-beam sonar technology. Early (before July 1) and late (after June 30) runs of Kenai River chinook salmon have been monitored acoustically since 1987. A 200 kHz split-beam sonar system has been used since 1995 to estimate numbers of migrating adult chinook salmon returning to their natal stream. From 1987 to 1994, a 420 kHz dual-beam sonar was used to generate similar estimates. We estimated the net upstream migration of chinook salmon from 16 May through 3 August 1997 to be 62,383. This estimate is comprised of 11,776 early-run and 50,607 late-run fish.