[en] Both general morphology and fine ultrastructure of membranes were investigated in macrophages derived from irradiated and normal mice. Notable differences were found between the two cell types. Irradiated macrophages contained numerous small invaginations or holes on their outer surfaces, while normal cells had few such structures. Scanning electron microscopy revealed that macrophages of mice irradiated in vivo with either 550 R or 800 R were round or elongated, respectively, while cells derived from nonirradiated animals displayed no uniformity in shape. (U.S.)