The effect of the antidepressant doxepin on cytosolic Ca^(2+) concentrations ([Ca^(2+)]_i) and viability in PC3 human prostate cancer cells was explored. The Ca^(2+)-sensitive fluorescent dye fura-2 was applied to measure [Ca^(2+)]_i. Doxepin at concentrations of 500-1000μM induced a [Ca^(2+)]_i rise in a concentrationdependent manner. The response was reduced partly by removing Ca^(2+). Doxepin-evoked Ca^(2+) entry was suppressed by Ca^(2+) entry blockers (nifedipine, econazole, SK&F96365), and protein kinase C (PKC) modulators. In the absence of extracellular Ca^(2+), incubation with the endoplasmic reticulum Ca^(2+) pump inhibitor thapsigargin or 2, 5-di-tert-butylhydroquinone (BHQ) partly inhibit doxepin-induced [Ca^(2+)]_i rise. Incubation with doxepin nearly inhibited thapsigargin or BHQ-induced [Ca^(2+)]_i rise. Inhibition of phospholipase C (PLC) with U73122 failed to alter doxepin-induced [Ca^(2+)]_i rise. At concentrations of 200-250μM, doxepin killed cells in a concentration-dependent manner. This cytotoxic effect was not reversed by chelating cytosolic Ca^(2+) with 1, 2-bis (2-aminophenoxy) ethane-N, N, N', N'- tetraacetic acid/acetoxy methyl (BAPTA/AM). Annexin V/PI staining data implied that doxepin (200 and 250μM) did not induce apoptosis. Collectively, in PC3 cells, doxepin induced a [Ca^(2+)]_i rise by evoking PLC-independent Ca^(2+) release from stores including the endoplasmic reticulum and Ca^(2+) entry via PKC-sensitive store-operated Ca^(2+) channels. Doxepin caused cell death that was independent of [Ca^(2+)]_i rises.