The polarographic reduction and parameter tg alpha of a series of natural and synthetic pyrimidine nucleosides, cytidine derivatives, and the cancerostatic agent arabinosylcytosine were studied. Correlations were found between these newly determined characteristics and capacity factor kappa from HPLC analysis, growth inhibition of E. coli B bacteria, deamination of nucleosides by cytidine deaminase, DNA synthesis, and rate of biotransformation and lipophilicity expressed as log P. It was confirmed that the molecule of nucleosides is complex to such an extent that no linear correlation could be revealed among the respective parameters. Linear correlation was found only in smaller, structurally similar groups of derivatives.