Cyclooxygenase-2 (COX-2) is involved in inhibition of apoptosis, potentiation of cell growth, and angiogenesis and as such is a target for drug development. The COX-2 enzyme is frequently overexpressed in pancreatic cancer. The aim of this study was to determine the effects of celecoxib on the growth inhibition and induction of apoptosis by gemcitabine in pancreatic cancer cell lines. Baseline expression of COX-2 enzyme was determined by Western blot analysis in five human pancreatic cancer cell lines. Cells were treated with gemcitabine (100 nmol/L), celecoxib (1, 10, and 50 micromol/L), and the combination. No potentiation in growth inhibition was observed in MIAPaCa cells (low COX-2 expression). However, growth inhibition and apoptosis were significantly increased with celecoxib in the BxPC-3 cells that have a high COX-2 expression. Significant down-regulation of nuclear factor-kappaB activation was observed in BxPC-3 cells treated with celecoxib and gemcitabine. Moreover, down-regulation of COX-2 mRNA and protein expression was also observed in the BxPC-3 cells treated with the combination as compared with the untreated and the celecoxib-treated and gemcitabine-treated cell lines. We conclude that celecoxib potentiates gemcitabine-induced growth inhibition and apoptosis in pancreatic cell lines. In addition to inhibition of the COX-2 enzyme, the celecoxib and gemcitabine combination down-regulated nuclear factor-kappaB activation, which in turn may have contributed to the induction of apoptosis and the down-regulation of transcription of the COX-2 enzyme.