We have studied the effects of sodium butyrate on DNA-mediated gene transfer in an effort to investigate interrelationships between chromatin structure and expression of recombinant plasmids. Our results demonstrate that butyrate affects the early stages of gene activity following DNA uptake at least two levels. First, the number of cells able to express foreign DNA increases from 10% to up to 40%. Second, there is an increase in enhancer-dependent transcription, approximately 30 fold in HeLa cells, involving the SV40 early promoter. Stable transformation efficiencies increase to 4% and 10% in HeLa S3 and monkey kidney CV-1 cells, respectively. Finally, expression of integrated recombinant plasmid genes is reinducible by a second treatment five weeks after initial exposure to this agent.