Estimation of anti-CMV-IgG and anti-CMV-IgM is considered a relatively inexpensive screening tool of CMV status. The aim of study was to estimate how the immunosuppressive protocol influence serum anti-CMV IgG and IgM concentration in renal graft recipients and to estimate the adequacy of anti-CMV-IgG concentration and anti-CMV-IgM index as screening parameters of active CMV disease in patients receiving different immunosuppression. The study group consisted of 33 patients with clinical signs of CMV disease who received one of three types of immunosuppression: (1) azathioprine (Aza) + cyclosporine (CyA) + prednisone (Pr), 20 patients; (2) mycophenolate mofetil (MMF) + CyA + Pr, eight patients; tacrolimus (Tac) + MMF, five patients. Patients were enrolled when the pp65-antigen (pp65) of PBL was positive within 1 to 5 months after transplant (75 patients tested). The IgM-i in the Aza + CyA + Pr group was higher than in MMF + CyA + Pr group (2.73 + 1.8 vs 1.08 +/- 1.07, P =.021). The IgM-i in the Aza + CyA + Pr group was higher than in Tac + MMF (2.73 +/- 1.8 vs 0.78 +/- 0.69; P =.014). There was no difference in IgM-i between MMF + CyA + Pr and Tac + MMF. There was no difference in relative increase of IgG-c among all groups but there was a difference in relative increase of IgM-i between Aza + CyA + Pr and MMF + CyA + Pr groups (6.7 +/- 9.4 vs 2.3 +/- 5.9; P =.007) and between Aza + CyA + Pr and MMF + Tac groups (6.7 +/- 9.4 vs 0.6 +/- 0.54; P =.003). Immunosuppressive protocols including MMF exert an inhibitory influence on B-cell response and synthesis of anti-CMV-IgM. It makes the anti-CMV-IgM index an inadequate rough screening diagnostic parameter of active CMV disease.