Cyclooxygenase-2 (COX-2) is an important target for the suppression of colorectal tumorigenesis by non-steroidal anti-inflammatory drugs (NSAIDs). To evaluate the role of COX-2 in human sporadic colorectal adenomas, COX-2 mRNA expression was examined by reverse transcription-polymerase chain reaction (RT-PCR) in 63 adenomas. COX-2 mRNA was detected in all the adenomas at higher levels than in normal colorectal mucosa (P<0.001). Levels of expression in the adenomas were correlated with their size (P=0.019), but no relationships were demonstrable between COX-2 expression and adenoma location, macroscopically observed configuration or microscopic degree of dysplasia. These findings suggest that COX-2 plays an important role in the growth of sporadic colorectal adenomas.