UV-A, the three compounds strongly inactivate T2 phage and inhibit epidermal DNA synthesis in mice. Moreover, they show a mutagenic activity markedly lower than that of 8-methoxypsoralen on Escherichia coli wild-type strain. Due to its lack of skin phototoxicity, its low mutagenic activity, and its antiproliferative activity, 2c was chosen for clinical evaluation. It proved to be effective in clearing