Pipes, which are relatively inexpensive and easily installed, are an economical and efficient solution to certain problems of fish passage at dams and at other obstacles blocking migratory routes. The purposes of this study (1963-1964) were to determine: (1) if adult salmon and trout at Bonneville Dam on the Columbia River would use a pipe as a passageway and (2) how the conditions at the entrance and within the pipe, diameter and length, illumination, and flow would influence passage. The pipes were 0.3, 0.6, and 0.9 m. in diameter and were 27.4 to 82.3 m. long. Chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (O. nerka), coho salmon (O. kisutch), and steelhead trout (Salmo gairdneri) passed through unilluminated pipes up to 82.3 m. long. Of the four species tested, only steelhead trout appeared to benefit appreciably from illumination. For distances up to 82.3 m., a 0.6-m.-diameter pipe was large enough to pass all salmon and trout. The fish passed through a 0.6 m.-diameter pipe when it was flooded or partly filled with water, but did not readily enter a 0.3-m. pipe until special conditions of water velocity and transition from pool to pipe were provided.