1. The sterol composition of three Palythoa species has been analysed and compared with literature data.The mixture of sterols known as "palysterol" has been observed in all our samples suggesting that palysterol might be considered as a fingerprint of Palythoa species.The sterols of Palythoa caribaeorum did not show marked geographic, seasonal or sex variations and its zooxanthella showed about the same sterol composition as the host symbiont association.Biological implications are discussed.