Compounds AT2433-A1 (Al), AT2433-A2 (A2), AT2433-B1 (Bl), and AT2433-B2 (B2) were isolated from the cultured broth of Actinomadura melliaura sp. nov. (SCC 1655). Structurally these materials are closely related to rebeccamycin (1), an indolocarbazole antitumor antibiotic. Al, A2, Bl, and B2 were active against Staphylococcus aureus A9537, Streptococcus faecalis A20688, Streptococcus faecium (ATCC 9790), Micrococcus lutea (ATCC 9341), Bacillus subtilis (ATCC 6633). Under a cooperative antitumor screening agreement between the Schering Plough Corporation and the Bristol-Myers Company, the culture Actinomadura melliaura (SCC 1655) was selected for further evaluation, leading to the discovery of these four novel, biologically active compounds. Al and Bl were active against P388 leukemia in mice. This paper describes the taxonomy of the producing strain, the fermentation, the purification and biological properties of Al, A2, Bl, and B2. Details of the structure determination will be reported elsewhere.