The pharmacokinetics of 3H-ZIMET 98/69 after i.v. and oral administration to rats was studied. After i.v. administration of 2.5 and 10 mg/kg a biphasic exponential decay of total serum radioactivity was found, so that a two compartment open model could be assumed. Oral administration of 10 mg/kg results only a moderate bioavailability (25%), which further decreased after administration of higher doses. The distribution steady state between serum and tissue is reached rapidly. Elimination proceeds slowly, the serum half-life being 64-84 h.