A method using polyethylene tubing of various sizes and a flow of water commensurate with the size of the specimen has been employed to determine the resting metabolic rates of large fish. With female dogfish, ranging in size from 0.1-9 kg, at about 13° C, there is a linear regression of log metabolic rate on log body weight with a slope calculated at 0.74. The metabolic rates of ling-cod, ranging in body weight from about 0.2-20 kg, gave a slope of 0.78.