Rabbit arterial smooth muscle cells were transfected with the pBC24neo plasmid DNA which consists of a sequence of 790 base pairs from the BglII N fragment of herpes simplex virus type 2 DNA linked to the neo resistance gene. Selection in G418-containing medium resulted in eleven immortalized clones which showed increased growth rate and saturation densities. One of the eleven clones maintained the transforming DNA sequence integrated in the cellular genome and showed continous resistance to G418, but Southern blot analysis of the other ten immortalized clones did not detect pBC24neo DNA sequences. Possible mechanisms of herpes simplex virus induced immortalization and their implications in the development of atheromatous plaques are discussed.