Renal mesangial cells regulate their expression of the pro-inflammatory gene cyclooxygenase-2 (COX-2) through mechanisms involving gene transcription and post-transcriptional events. Post-transcriptional regulation of COX-2 is dependent, in part, on sequences within the 3′-untranslated region (3′-UTR) of the COX-2 mRNA. Insertion of the entire 3′-UTR of COX-2 into the 3′-UTR of luciferase resulted in a 70% decrease in luciferase enzymatic activity. Measurement of steady-state reporter gene mRNA levels suggested that the loss of activity was due to decreased translational efficiency. Deletion analysis identified the first 60 nucleotides of the 3′-UTR of COX-2 as a major translational control element. This region of the 3′-UTR of COX-2 is highly conserved across species; is AU-rich; and contains multiple repeats of the regulatory sequence AUUUA, reported to confer post-transcriptional control. In addition, we identified regions of the 3′-UTR of COX-2 outside of the first 60 nucleotides that altered message stability. Some of these regions contained AUUUA consensus sequences, whereas others did not, and represent novel control elements. These results suggest that expression of COX-2 in mesangial cells depends on the complex integration of multiple signals derived from the 3′-UTR of the message.