Analysis of purified naked and enveloped nucleocapsids of pseudorabies virus with high-resolution techniques has allowed a reassessment of their protein composition. Enveloped particles are shown to contain at least 20 proteins whose molecular weights are in the range 20,000 to 230,000. Naked nucleocapsids contain one major and seven minor proteins in the molecular weight range 20,000 to 155,000. Phosphorylation of at least one virion protein is shown to take place in vivo. These results demonstrate that pseudorabies virus is similar in its protein complement to other herpesviruses which have recently been examined.