DNA polymerase activity was determined in hyperkeratotic epidermis of the guinea pig by topical application of n.hexadecane. Epidermal cells were separated by Percoll gradient centrifugation. DNA polymerase alpha activity was higher in the basal cells, but polymerase beta activity was higher in granular cells than in cells from the other layers. The hyperkeratosis was accompanied by an increase in polymerase alpha activity in both the squamous and basal cells. However, polymerase beta activity decreased in the granular cells and was distributed almost uniformly across the epidermis. The distribution pattern of polymerase activities in the hyperkeratotic epidermis was not simply an enhancement of the pattern in normal epidermis.