We investigated the effect of n-butyrate (2.5 mM) on expression of the c-erb A oncogene in human colon fibroblasts. Exposure of these cells to the compound for 48 hours resulted in an increased accumulation of approximately 2.0 kb RNA which hybridized to a v-erb A cDNA probe. Hybridization to a beta-actin gene probe was unaffected by the treatment. This report is the first demonstration of a factor affecting expression of the c-erb A oncogene.