A series of bis(11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides) linked through the 6-carboxamides were prepared by coupling the requisite acid imidazolides with various diamines. Compounds with mono-cationic linker chains were more potent cytotoxins than the corresponding monomer in a panel of rodent and human cell lines, while those with the dicationic linker chains (CH2)2NR(CH2)2NR(CH2)2 and (CH2)2NR(CH2)3NR(CH2)2 showed extraordinarily high potencies (for example, IC50s of 0.18-1.4 nM against human Jurkat leukemia; up to 1000-fold more potent than the parent monomer). As seen previously in the monomeric series, small, lipophilic 4-substituents significantly increased potency in cell culture. The dimeric compounds were all slightly to significantly more potent in the mutant JL(A) and JL(D) cell lines that under-express topo II, suggesting that this enzyme is not their primary target. An 11-imino-linked dimer was much less active, and an asymmetric indeno[1,2-b]quinoline-6-carboxamide/naphthalimide dimer was less active than the comparable symmetric bis(indeno[1,2-b]quinoline-6-carboxamide). Selected analogues were active against sub-cutaneously implanted colon 38 tumors in mice, giving growth delays comparable to that of the clinical topo I inhibitor irinotecan at up to 10-fold lower doses. These compounds form an interesting new class of putative topo I inhibitors.