Abstract The structural components of purified enveloped virions and of purified nucleocapsids of the tissue culture strain (L-M cell) of equine herpes virus type 1 (EHV-1L) were analyzed by discontinuous sodium dodecyl sulfate polyacryalmide gel electrophoresis. Enveloped virions were comprised of 28 structural proteins of average molecular weights ranging from 270,000 to 16,000. Twelve of the proteins exhibited molecular weights of greater than 100,000, and six of these were above 200,000. Utilizing radioactively labeled compounds ( 3H-glucosamine and 3H-choline), four glycoproteins, four lipoproteins, and nine glycolipoproteins were shown to be present in the virions. Purified nucleocapsids, isolated from nuclear extracts of infected L-M cells, contained five major structural proteins with average molecular weights of 148,000, 59,000, 46,000, 36,000, and 18,000. These five proteins comprised greater than 96% of total nucleocapsid protein, on the basis of radioactivity. The 148,000 MW protein (VP 9) accounted for approximately 65% of the total nucleocapsid protein and was the major structural protein of both nucleocapsids and intact virions. None of these proteins corresponded to glycoproteins or lipoproteins present in enveloped virions, indicating that glycoproteins and lipoproteins are components of the envelope. The remaining 4% consisted of eight structural proteins ranging from 140,000 to 30,000 MW and were judged to be minor structural components, reproducibly present in all preparations of nucleocapsids.