The synthesis of lipids in BSC 1 cells and their association with herpes simplex virus was studied. Radioactive choline was found to be incorporated mainly into lecithin. Infection of cells with herpes simplex virus did not affect the synthesis of cellular lipoproteins. Infected cells, prelabelled with radioactive choline, yielded virus particles which contained radioactively labelled cellular lipids. Treatment of herpes virus particles with sodium deoxycholate caused the dissociation of the particles and the release of capsomeres and soluble proteins.