Posttranslational processing of vaccinia virus proteins has proven to be a common mechanism for exerting regulatory control of function or targeting to subcellular and/or subviral structures. Fatty acylation, most commonly observed as the addition of myristate or palmitate, occurs on numerous vaccinia proteins and affects each in a distinct manner. Labeling of vaccinia-infected cells with tritiated myristic or palmitic acids demonstrates that vaccinia encodes at least six myristylproteins and six palmitylproteins. Where investigated, each of these proteins have been demonstrated to play important roles in the virus life cycle. Likewise, in each case studied, the fatty acyl modification greatly influences the function and/or biological activity of the protein.