The heat shock (HS) response is a conserved cellular defense mechanism to elevated temperatures, observed in cells from bacteria to human. It is characterized by the increased accumulation of HS proteins. This work examines the effect of HS on the secondary metabolite biosynthesis of cultured plant cells. Suspension cultures of Taxus yunnanensis cells, which produce the anticancer diterpenoid paclitaxel (Taxol (R)), were heat shocked at 35-50 degrees C for 30-60 min. The results show that HS reduced cell viability and growth but significantly induced paclitaxel production. The HS-induced paclitaxel production depended on the intensity of HS and the physiological state of the cells. Abscisic acid (ABA)-pretreatment not only increased cell viability and growth upon HS but also improved HS-induced paclitaxel yield. The best culture phase to apply the HS was the late-exponential growth phase. Under the optimized condition, HS enhanced paclitaxel yield by sixfold to 6.8 mg/L. In addition, a prior mild-HS treatment also significantly increased HS-induced paclitaxel production. Furthermore, HS induced oxidative burst, the early event of plant defense response to pathogen attack and other stress challenge; the addition of putative inhibitors of lipoxygenase, a key enzyme for jasmonic acid biosynthesis, significantly inhibited HS-induced pacliatxel accumulation. The stimulation of secondary metabolite production by HS may be a result of HS-induced plant cell defense response.