EC-MPS is a delayed release formulation of mycophenolic acid (MPA) developed to deliver MPA to the small intestine and reduce upper gastrointestinal tract adverse-effects. The primary objective of this study is to compare pharmacokinetics (PK) of MMF plus FK with PK of EC-MPS plus FK. We studied a group of 32 stable RT patients treated with FK and MMF without steroids. 53% were men. Age x: 56.5y (31-76). Time from RT x: 5.5y (1.2-21.7). MMF doses x: 1.02g/d (500mg-2g) Target C_min (1.5-4ng/L). FK doses x: 4.7mg/d (2-12.5) Target C_min (8-11ng/L). We determined simultaneously the 12-hour plasma MMF and FK PK profile. Next, patients were switched to equimolar doses of EC-MPS. After 30 days a new PK profile of EC-MPS and FK was carried out. The following PK parameters were considered for each drug: predose concentration (C_min), maximum concentration (C_max), time of maximum concentration (T_max) and the AUC calculated by the trapezoidal rule. FK and MMF doses remained stable throughtout the study, no patient was on rifampicin, AAS, antacids or cholestyramine during the study period. S.Cr, proteinuria and S.albumin before and after conversion were 1.6 0.48mg/dl, 189 102mg/d, and 4.2 0.33mg/dl and 1.58 0.49-mg/dl, 201 147mg/d, and 4.18 0.34mg/dl respectively. Leukocites, hemoglobin and platelets before and after conversion were 6.85 2.16, 13.3 1.6mg/dL and 202 63 and: 7.40 2.83, 13.1 1.6mg/dL and 213 67 respectively. Bilirrubin before and after conversion was 0.63 0.21mg/dl and 0.61 0.22mg/dl respectively. FK Tmax, Cmin and CV%, were equivalent with MMF and with EC-MPS. FK Cmax and AUC were 20% and 18% lower with MPS (p=0.0013). MPA Cmin, Tmax, Cmax, and AUC were 18%, 27% (p=0.0013), 36% (p=0.0013), and 27% (p<.001) higher with MPS. Neither acute rejection episodes nor oportunistic infections were observed. No one patient complained of new-onset GI side-effects and no doseadjustements were needed. In stable RT patients treated with FK, MMF can be switched to equimolar doses of EC-MPS taking into account that although FK Cmin concentration is not different, FK AUC is significantly lower with MPS. At equimolar doses, MPS provides significantly higher AUC, Cmax and Cmin than MMF. These PK discrepancies were without short term clinical significance i.e. acute rejection or oportunistic infections. S.creatinine, daily proteinuria, bilirrubin and hematological parameters showed no significant changes. G.I. tolerance after switching to MPS was excellent.