The purpose of this research was to determine the effects of retinoic acid on bovine papillomavirus (BPV) transformed cells. Since BPV transformed cells are able to form colonies in agar and their untransformed counterparts are not, of particular interest was the effect of retinoic acid on this marker. Retinoic acid inhibited the growth of colony forming cells, but the extent of inhibition varied among several cloned cell lines. Retinoic acid inhibited the proliferation of BPV transformed cells and the extent of this inhibition also varied. The copy number of the virus was determined for each of three cell lines by liquid reassociation experiments. The copy number did not change when the cells were treated with RA for a prolonged period of time. Gel electrophoresis and Southern blotting of extrachromosomal DNA from the cell lines revealed the presence of unit length BPV DNA in all three transformed cell lines. The amount of BPV DNA per cell was decreased when the cells were treated with 10⁻⁵ M RA for three days.