An indolo[2-3-b]quinoxaline derivative represented by general formula (I) (wherein one of R¹ and R² represents hydrogen and the other represents -CH₂NHCCH₃(CH₂OH)₂, etc.; and R³ represents hydrogen, methyl, etc.) or a pharmaceutically acceptable salt thereof has an antitumor effect and therefore is useful as a drug.
Indolo[2,3-b]quinoxaline derivatives represented by the following formula: ##STR1## wherein one of R.sup.1 and R.sup.2 is a hydrogen atom and the other is a group of the formula: --CH.sub.2 NHCCH.sub.3 (CH.sub.2 OH).sub.2, etc, and R.sup.3 is a hydrogen atom, a methyl group, etc.; and pharmaceutically acceptable salts thereof have an antitumor activity and are useful as medicines.