The role of cyclooxygenase-2 (COX-2) in cancer remains controversial. Using cervical carcinoma cells (HeLa), the present study investigates the involvement of COX-2 in apoptosis elicited by the chemotherapeutics paclitaxel, cisplatin and 5-fluorouracil. Each compound led to a profound induction of COX-2 expression and prostaglandin (PG) synthesis, accompanied by a substantial decrease of viability and enhanced apoptosis. Cells were significantly less sensitive to apoptotic death when either COX-2 expression or its activity was suppressed by small-interfering RNA (siRNA) and by the selective COX-2 inhibitor NS-398, respectively. Experiments performed to clarify how COX-2 leads to apoptosis revealed a profound proapoptotic action of PGD2 and its dehydration product, 15-deoxy-Delta(12,14) PGJ2 (15d-PGJ2). In line with these findings, chemotherapeutics-induced apoptosis was prevented by siRNA targeting lipocalin-type PGD synthase (L-PGDS), which catalyses the isomerization of PGH(2) to PGD2. Moreover, apoptosis by chemotherapeutics, PGD2 and 15d-PGJ2 was suppressed by the peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW-9662 or PPARgamma siRNA. Finally, a COX-2-dependent apoptotic mechanism of all investigated chemotherapeutics was confirmed in human lung cancer cells (A549) as well as in another cervical carcinoma cell line (C33A). Collectively, this study suggests COX-2 induction and synthesis of L-PGDS-derived, PPARgamma-activating PGs as a decisive target by which several chemotherapeutics induce apoptosis. COX-2 is therefore suspected to sensitize cancer cells to apoptotic death under certain circumstances, suggesting that COX-2 inhibition during cancer therapy could diminish its efficacy.