Biologic Action Spectra of 8-Methoxypsoralen Determined by Monochromatic Light *

It is well known that certain of the natural furocoumarins extend the range of effective ultraviolet wavelengths beyond 320 nm and produce intense erythematous reactions with normally harmless long ultraviolet (1-8). Although it has been consistently observed that 8-methoxypsoralen (8-MOP) activates long ultraviolet there have been few studies to determine the wavelengths at which it is most effective.