Diallel crosses were made among Coregonus clupeaformis (Mitchill), Leucichthys artedii LeSueur and Prosopium cylindraceum (Pallas). Embryos of the crosses Coregonus ♂ X Leucichthys ♀, Coregonus ♂ X Prosopium ♀, and Leucichthys ♂ X Coregonus ♀ completed development and hatched. This is the first known instance of successful hybridization between the genera Coregonus and Prosopium. Embryos of crosses Leucichthys ♂ X Prosopium ♀, Prosopium ♂ X Coregonus ♀, and Prosopium ♂ X Leucichthys ♀ passed through a considerable portion of their development, but all died prior to the expected time of hatching. Embryos of these three crosses were invariably deformed.