Scanning electron microscopy and immunofluorescence techniques show that the attachment of adenovirus type 5 to HeLa cells is followed by a temperature-dependent redistribution of virus particles on the cell surface. Metabolic inhibitors and cytochalasin B, a drug that impairs microfilament function, blocked this redistribution. Transmission electron microscopy studies demonstrated that inhibition of redistribution was paralleled by an inhibition of virus internalization. In further experiments virus and cells were incubated at 4 degrees C and then treated with adenovirus 'soluble' antigens to block unoccupied virus receptors. On warming these preparations to 37 degrees C, the internalization of attached virions was found to be impaired. It is proposed that energy-dependent redistribution of attached adenovirus particles on the cell surface facilitates entry by bringing virions into contact with sufficient receptors to allow internalization.