Free fatty acids exhibit diverse biological effects such as the regulation of immune responses in humans and animals. To investigate the biological effect of fatty acids in the model eukaryotic organism yeast, we examined the activity of various fatty acids in a yeast-based drug-screening system designed to detect the small-molecule compounds that inhibit Ca(2+)-signal-mediated cell-cycle regulation. Among the fatty acids examined, ricinoleic acid markedly alleviated the deleterious physiological effects induced by the compelled activation of Ca(2+) signaling by external CaCl(2), such as the polarized bud growth and the growth arrest in the G(2) phase. In accordance with the physiological consequences induced by ricinoleic acid, it diminished the Ca(2+)-induced phosphorylation of Cdc28p at Tyr-19, concomitant with the decrease in the Ca(2+)-stimulated expression levels of Cln2p and Swe1p.