Rebeccamycin analogues containing one azaindole unit, with and without a methyl group on the imide nitrogen and with the sugar moiety coupled either to the indole nitrogen or to the azaindole nitrogen were synthesized. To increase the solubility and induce stronger interactions with the target macromolecules, a bromo or nitro substitutent was introduced on the indole unit. The DNA binding and topoisomerase I inhibition properties were investigated together with the antiproliferative activities toward nine tumor cell lines. In addition, the effect of the compounds on the cell cycle of L1210 leukemia cells was examined. The nonaza analogues were found to be cytotoxic against all cell lines of the panel whereas the aza-analogues showed a selective action toward certain cell lines. They strongly inhibited the proliferation of SK-N-MC neuroblastoma, A431 epidermoid carcinoma and NCI-H69 small cell lung carcinoma cells, but showed little or no cytotoxic effect against IGROV ovary carcinoma, HT29 colon carcinoma, and A549 non small cell lung carcinoma cells. Whatever their cytotoxicity profile, all compounds induce similar cell cycle effects, with a marked G2+M block observed with L1210 leukemia cells. The data suggest that the molecular mechanism of action of the aza-analogue derivatives is different from that of rebeccamycin.