The nuclear DNA contents of 22 salmonid taxa, estimated primarily by flow-cytometric analysis relative to a chicken internal standard, were evaluated to compare intra- and interspecific variation in DNA content within this fish family. The average variability within taxa exceeded that among taxa. Intraspecific genome-size variation was substantial and, in some cases, exceeded the mean genome size for the species. The flow-cytometric method used here allows for rapid and reliable comparison of nuclear DNA contents within and among individuals from natural animal populations.