Three representative cytokines interleukin (IL-8), RANTES and tumour necrosis factor alpha (TNF-alpha) have a concentration-dependent chemotactic effect on the unicellular Tetrahymena. Maximal effective concentrations of IL-8 (1 ng/ml) and RANTES (75 ng/ml) are in the same range as in mammals, which indicates an evolutionary background of physiological effects elicited. Progeny generations of cells selected for their affinity to cytokines (IL-8 and TNF-alpha) show an enhanced positive chemosensory reaction to the cytokines. The changed reaction of these cells to the chemoattraction of the culturing medium was also observed. The results call attention to the presence of cytokine-dependent processes at a low phylogenetic level.