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 mμ in length and 193.8μ in width. The C form was not beaded, had a serrated periphery and averaged 352.8 mμ in length and 196 mμ in width. A short discussion of the morphology of seal poxvirus in relation to other poxviruses is presented.