Pharmacokinetic parameters of MPA and MPAG will be determined by noncompartmental methods. The area under the plasma concentration-time curve from time 0 to 12 hours (AUC) will be calculated by the trapezoidal rule. Maximum serum concentration (Cmax) and time to reach Cmax (Tmax) will be determined from visual inspection of the concentration-time profile. Clearance (CL/F) will be calculated by dose divided by AUC. Samples will be obtained to measure IMPDH and correlated with PK parameters. These tests will be assayed by Les Shaw at the University of Pennsylvania.