Prostaglandins (PGs) and thromboxane (TX) are important mediators of inflammation. Recent studies revealed that PG and TX synthesis is controlled by the regulation of PG‐ and TX‐synthesizing enzymes. In this study, we examined the TX synthesis and the expression of TX‐synthesizing enzymes in activated peripheral polymorphonuclear leukocytes (PMNs) obtained from children with bacterial infection. Blood samples were obtained from controls and patients with bacterial infection. A23187‐stimulated production of TXB₂, a stable metabolite of TXA₂ in PMNs, was measured by a specific radioimmunoassay. The mRNA expression of cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase (COX)‐1, COX‐2, and TXA₂ synthase was determined by RT‐PCR. The synthesis of TXB₂ in PMNs was significantly increased in the patients [925.0 (550.0–1100.0) pg/10⁶ cells], compared with the controls [550.0 (450.0–775.0) pg/10⁶ cells]. The mRNA expression for cPLA₂ and COX‐2 in PMNs was also enhanced in the patients. The results indicate that TX production in PMNs is significantly increased through possible transcriptional mechanisms of cPLA₂ and COX‐2 during bacterial infection in children. The upregulation of TXA₂ synthesis may contribute to the process of acute inflammatory reaction caused by bacterial infection. Am. J. Hematol. 72:115–120, 2003. © 2003 Wiley‐Liss, Inc.