New batracylin conjugates with tuftsin/retro-tuftsin derivatives were designed and synthesized using T3P as a coupling agent. The conjugates possess an amide bond formed between the carboxyl group of heterocyclic molecule and the N-termini of the tuftsin/retro-tuftsin chain. The in vitro cytotoxic activity of the new analogues and their precursors was evaluated using a series of human and murine tumor cells. BAT conjugates containing retro-tuftsin with branched side aminoacid chain, in particular with leucine or isoleucine, were about 10-fold more cytotoxic toward two human tumor cell lines (lung adenocarcinoma (A549) and myeloblastic leukemia (HL-60)). These compounds showed about 10-fold increased cytotoxicity against the two types of tumor cells compared to parent BAT. We have not observed important differences in the mechanism of action between BAT and its cytotoxic tuftsin/retro-tuftsin conjugates. We propose that high biological activity of the most active BAT conjugates is a result of their greatly increased intracellular accumulation.