The fine structure of the M and C forms of seal poxvirus as observed in negative stained preparations in the electron microscope are described. The M form has a beaded surface and a serrated outline and particles averaged 312.3 mmicro, in length and 193.8 microns in width. The C form was not beaded, had a serrated periphery and averaged 352.8 mmicro in length and 196 mmicro in width. A short discussion of the morphology of seal poxvirus in relation to other poxviruses is presented.