The preparation and cytotoxic properties of 4,11-dihydroxynaphtho[2,3-f]indole-5,10-dione derivatives carrying N-aminoalkyl substituents are described. The N-aminobutylnaphthoindolediones obtained were studied in National Cancer Institute Screening Program and demonstrated high antiproliferative activity against 60 human cancer cell lines. All N-(4-aminobutyl) derivatives have higher potency than adriamycin or mitoxantrone against adriamycin selected multidrug resistant breast cancer cell line NCI/ADR.