The synthesis and some biological properties of 4-hydroxymethyltetrahydro- and 4-hydroxymethylbenzopsoralen are reported. The two compounds exhibited activity in the dark and by UVA irradiation. The tetrahydrobenzo derivative was more effective than the corresponding aromatic compound. Benzopsoralens were more cytotoxic in malignant (HL60 and HeLa) cell lines than in normal ones (NCTC 2544). Their toxicity decreased in confluent cultures of NCTC 2544 cells.