This is the ®rst detailed analysis of the cell cycle
responses of melanocytes and keratinocytes in human
skin to UVR. We have observed increased BrdU
incorporation during the ®rst 24 h following irradiation,
suggesting that UVR is acting as a mitogen,
stimulating a rapid round of DNA synthesis. The
reduced BrdU labelling from 24 ± 48 h demonstrated
that cells did not re-enter S phase during this period.