In human osteosarcoma MG63 cells, effect of triethyltin, an environmental toxicant, on intracellular Ca2+ concentration ([Ca2+]i) was measured by using fura-2. Triethyltin (1–50 μM) caused a rapid and sustained plateau rise of [Ca2+]i in a concentration-dependent manner (EC50=10 μM). Triethyltin-induced [Ca2+]i rise was prevented by 50% by removal of extracellular Ca2+ but was not altered by voltage-gated Ca2+ channel blockers. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca2+-ATPase, caused a monophasic [Ca2+]i rise, after which the increasing effect of triethyltin on [Ca2+]i was attenuated by 60%; also, pretreatment with triethyltin abolished thapsigargin-induced [Ca2+]i increase. Depletion of mitochondrial Ca2+ with carbonylcyanide m-chlorophenylhydrazone (CCCP; 2 μM) did not affect triethyltin-induced Ca2+ release. U73122, an inhibitor of phoispholipase C, abolished ATP (but not triethyltin)-induced [Ca2+]i rise. A low concentration (1 μM) of triethyltin failed to alter ATP and bradykinin-induced [Ca2+]i rises. These findings suggest that triethyltin rapidly increases [Ca2+]i in osteoblasts by stimulating both extracellular Ca2+ influx and intracellular Ca2+ release via as yet unidentified mechanism(s).