Human 293 cells, transformed by and expressing the early region of the adenovirus genome (i.e., E1A and E1B), contain a phase-dense cytoplasmic structure situated in close proximity to the nucleus. Via indirect immunofluorescence studies such structures have been previously shown to contain both the adenovirus E1B (55 kDa) protein as well as the tumor suppressor gene product p53. Here we show that such structures also stain positive for the cytoplasmic hsp 70 proteins. Such phase-dense structures containing hsp 70, p53, and adenovirus E1B are not unique to 293 cells but also are observed in rodent cell lines stabily transfected with the early region of the adenovirus genome. Using an antibody against a centrosomal protein, pericentrin, we show that these cytoplasmic phase-dense structures are in close proximity to the centrosome. Cell fractionation studies revealed such structures to be highly detergent insoluble. However, like the centrosome, the cytoplasmic phase-dense structures could be rendered detergent soluble following treatment of the cells with agents that disrupt the integrity of the cytoskeleton. While the phase-dense structures appear in close proximity to the centrosome in interphase cells, during mitosis the centrosome and the phase-dense bodies separate from one another. Owing to these observations we examined whether hsp70 and p53 might also co-localize with the centrosome in other cell types not expressing the adenovirus E1A/E1B proteins. We show that a portion of both hsp70 and p53 indeed are present within the centrosome in Hela, COS, and 3T3 cells. These observations raise the possibility that components like hsp70 and p53 may participate in the mechanism(s) controlling cell division in mammalian cells.