A direct, acid-catalyzed substitution reaction incorporates an N-phthalimidomethyl group on the 4' or 5' carbon of a psoralen in yields of 60-80% via the condensation of an N-hydroxymethylamide or phthalimide (e.g. N-hydroxymethylphthalimide) and an appropriately substituted psoralen. The phthalimide moiety is cleaved from the psoralen ring by treatment with hydrazine to give 60 to 70% yields of the aminomethylpsoralens.