The organization, synthesis, and phosphorylation of vimentin were studied at various times after infection of monkey kidney cells with simian virus 40. Late after infection (between 36 and 48 h postinfection) there is a dramatic reduction in vimentin synthesis that is paralleled by a specific disruption of the intermediate filament network. At the same time there is no apparent alteration of the organization or the synthesis of the actin-containing filaments and of the microtubules. The inhibition of vimentin synthesis is also reflected by the level of vimentin mRNA activity in the infected cells, as assayed in a cell-free in vitro translation system, and vimentin mRNA concentration as revealed by RNA blot hybridization to cloned vimentin cDNA. The level of vimentin phosphorylation also decreases dramatically but at a much earlier time after infection (between 14 and 24 h postinfection), when mitosis in the infected cells is blocked. Although the decrease in vimentin synthesis in simian virus 40-infected cells is paralleled by the alterations in the organization of the intermediate filament network, the phosphorylation of vimentin correlates with the cell cycle, as it does in other systems. A possible feedback control mechanism of vimentin synthesis by alterations in the organization of the intermediate filament network is discussed.