The production of 5'-IMP and 5'-GMP by enzymatic conversion from RNA using a continuous two packed-bed reactor was investigated. 5'-Phosphodiesterase (5'PD) and 5'-adenylate deaminase (5'AD) were immobilized in an acrylic resin to produce derivatives with about 15 U/g of support. The kinetic properties of the enzymes were described by Michaelis-Menten models: no significant differences were found in the K m value of the free and immobilized 5'AD (60 and 20 μM, respectively), whereas for 5'PD the K m value was one order of magnitude higher for the immobilized enzyme (4.85 mg RNA/ml), probably due to diffusional limitations. Both enzymes remained stable after 8 h of use in a continuous packed-bed reactor whereas the half lives of the free enzymes were 193 min and 240 min at 40°C and 70°C for 5'AD and 5'PD, respectively. A procedure is proposed for the design of a continuous two packed-bed column process.