Eight psoralens have been evaluated for their ability to inhibit the in vitro growth of three human turner cell lines representing different tumor types, MCF-7 (breast cancer), NCI-14460 (non-small cell lung cancer) and SF-268 (CNS cancer). The synthesis of four new psoralens (benzofur-ocournarins) is presented as well as the results of the ab initio calculations to find the parameters that relate the structure with the antitumor activity. This work provides supplementary information that could allow the development of new psoralen analogues with this type of biological activity.For financial support from Fundação para a Ciência e Tecnologia, Portugal (I&D no. 226/9 and to CQ-UM), POCTI and FEDER; Ph.D. grants from FCT: Ana M.A.G. Oliveira (PRAXIS XXI/BD/19707/99), Madalena Pedro (SFRH/BD/1456/2000) and César Portela (SFRH/BD/3036/2000). For financial support and research grants to FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) and CNPq (Conselho Nacional do Desenvolvimento Científico e Tecnológico, Brazil). The authors thank National Cancer Institute, Bethesda, MD (USA) for kindly providing the tumor cell lines and Elisa Pinto for obtaining 1H-NMR and 13C-NMR spectra and elemental analyses.POCTI