Four series of diethylaminoalkoxyderivatives of coumarin (at the positions 4 and 7) and furocoumarin (at the positions 5 and 8) have been prepared, in order to study their complexing capacity with DNA, these compounds having a double possibility of interaction, that is intercalation of the aromatic moiety between two base pairs and formation of an electrostatic bond between their terminal amino group and a phosphoric group of DNA. Some biological effects connected with the interaction with DNA have also been studied. The results obtained showed that coumarin derivatives have a low complexing capacity and lack any biological activity. The furocoumarin derivatives showed a markedly increased complexing capacity both in respect to the coumarin derivatives and to the parent furocoumarin (psoralen, as well as its 5- and 8-methoxy derivatives) and proved able to inhibit DNA and RNA synthesis in Ehrlich ascites tumor cells, as well as the growth of Staphylococcus aureus and of various strains of Escherichia coli. This activity was generally low but was constantly higher in 5-than in 8-derivatives, the same behavior being found with regard to the complexing capacity with DNA. A good correlation between the ability to form complexes with DNA and the capacity to inhibit cells growth was clearly evidenced.