Abstract: The plasma concentration, metabolic clearance rate (MCR) and production rate (PR) of cAMP in probenecid treated rats (100mg/kg BW) have been measured by tracer kinetic method and protein competitive binding assay. The plasma concentration, MCR and PR of cAMP in probenecid treated rats were 26.7±2.9 pmol/ ml, 2.63±0.30ml/min/100g BW and 70.1±11.1 pmol/min/100 g BW (mean±SE), respectively, while the corresponding normal values were 48.4±5.3, 4.80±0.41 and 213.7±25.7, respectively. The differences between control and probenecid treated groups were very significant. These results suggest that probenecid is a metabolic blocker, of cAMP. Therefore when probenecid is used, the interferences due to change of cAMP metabolism should be considered.