The interaction of 20 anticancer drugs with cytosine was studied by charge-transfer reversed-phase thin-layer chromatography. The hydrophobicity, the specific hydrophobic surface area and the relative strength of interaction was calculated. Significant linear correlation was found between the hydrophobicity and specific hydrophobic surface area of drugs; this means that, from the chromatographic point of view, they form a homologous series of solutes. Only eight anticancer drugs showed significant interaction with cytosine. The binding of these drugs to cytosine (and possibly to other nucleotides) might be an important interaction which plays a role in the biological activity of drugs.