None supplied. Introduction: The seaward migration of salmonid smolts was monitored by the National Marine Fisheries Service (NMFS) at four sites on the Snake-Columbia River system in 1988. This project is part of the continuing Smolt Monitoring Program to monitor Columbia Basin salmonid stocks coordinated by the Fish Passage Center (FPC) for the Columbia Basin Fish and Wildlife Agencies and Indian Tribes. This program is carried out under the auspices of the Northwest Power Planning COuncil Fish and Wildlife Program and was funded by the Bonneville Power Administration (BPA). Sampling sites were Lower Granite, McNary, John Day, and Bonneville Dams. Data from these sites provided information required by the Fish Passage Managers (FPM) of the FPC for flow and spill management for fish passage during the migration season. Post season analysis of this information by the FPC provides travel time and migration timing information. Smolt Passage was monitored at these sites by: (1) systematic sampling of the smolt migration from late March through late July at the Lower Granite Dam, late March through late September at the McNary Dam, April through October at John Day Dam, and mid March through late November at Bonneville Dam; (2) recording brands; and (3) daily reporting of all pertinent fish capture and condition data, as well as dam operations and river flow data for passage estimates and travel indices to the FPC Fish Passage Data Information System (FPDIS).