The rate of 90Sr2+ deposition in Galaxea fascicularis was linear with respect to Sr2+ concentration (0.01–20 mM) and refractory to DCMU (1 μM), an inhibitor of photosynthesis. The deposition rate of 90Sr2+ in polyps incubated under a light intensity of 200 μE.m−2 s−2 was not significantly different from that in polyps incubated in total darkness. The deposition rate of 45Ca2+ (1–20 μM), on the other hand, exhibited saturation kinetics. In addition, it was DCMU sensitive and enhanced by light. Our results therefore support observations reported elsewhere that KsrA is inversely correlated with growth rate in reef corals. However, Sr2+ and Ca2+ deposition in G. fascicularis does not appear to involve similar biochemical mechanisms.