Novel cationic compounds forming complexes with oligodeoxyribonucleotides (ODNs) were prepared, and their ability to transport ODNs into cultured primary leukemic cells was tested. Two cationic porphyrin derivatives (2 and 3) were found to be at least 1 order of magnitude more efficient in this respect than commercially available agents. The ODN transporting capacity of novel compounds was dependent on the magnitude and the nature of their positive charges as well as on the porphyrin/ODN molar ratio. Porphyrin-ODN complexes were internalized into cells, and their dissociation was demonstrated by accumulation of fluorescein isothiocyanate-ODN fluorescence in the nucleus. Importantly, porphyrin 3 significantly protected complexed ODN against degradation and efficiently mediated the specific antisense effect on targeted v-Myb expression, resulting in reproducible growth inhibition of treated cells. Low toxicity, serum compatibility, and water solubility of porphyrin 3 make this compound a promising novel tool for modulation of gene expression in primary leukemic cells.