Compounds which are benzoheterocyclic distamycin derivatives of formula (I), wherein n is 2, 3 or 4; A is a heteroatom selected from O and S or is a group NR, wherein R is hydrogen or C.sub.1 -C.sub.4 alkyl; B is CH or N; R.sub.1 is hydrogen or C.sub.1 -C.sub.4 alkyl; G is selected from the group consisting of (a, b, c, d, e, f, g, h, i, j), and --C.ident.N; wherein R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are, independently from each other, hydrogen or C.sub.1 -C.sub.4 alkyl; T is a group of formula (II) or (III) as defined above, wherein p is 0 or 1; R.sub.2 and R.sub.3 are, independently from each other, hydrogen, C.sub.1 -C.sub.4 alkyl optionally substituted by one or more fluorine atoms, or C.sub.1 -C.sub.4 alkoxy; R.sub.4 is C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.3 haloalkyl; X.sub.1 and X.sub.2 are halogen atoms or pharmaceutically acceptable salts thereof; provided that at least one of R.sub.5, R.sub.6 and R.sub.7 is alkyl; are useful as antitumor agents. ##STR1## ##STR2##