The antitumour activities of four triorganophosphinegold(I) thiolates, R3PAu(SR) [R = Ph, Cy, Et; SRH = 6-mercaptopurine and R Et; SRH = 6-thioguanine] against the National Cancer Institute (NCI) panel of 60 cell lines are reported The [Cy3PAu(6-MP)] complex proved to be the more cytotoxic of the four complexes tested. For the 6-MP series, an order of cytotoxicity was established such that the activity followed the order R = Cy > Ph > Et. Sub-panel selectivity against the Leukemia cell lines was found for each of [Cy3PAu(6-MP)] and [Et3PAu(6-TG)].