A method for obtaining uniform fixation of whole bodies of fish for electron microscopic study is described. The procedure employs vascular perfusion of aldehyde fixatives through the proximal aorta of anesthetized fish. Light microscopic examination of semi-thin (0.5–1 μ) sections of Epon embedded material, stained with toluidine blue, showed near to complete removal of blood cells from vessels of gill, bone, skin, skeletal muscle, heart, exocrine pancreas, mesentery, glomerulus, and brain. Electron microscopic examination of liver and kidney, fixed by whole body perfusion, showed excellent preservation of cell ultrastructure.