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The pharmacokinetics of oxalate were studied in normal and nephrectomized rats with the use of radioisotope-labelled oxalate. The disappearance of [14C]oxalate from the plasma was analyzed with a two-compartment open model. The pharmacokinetic parameters of oxalate were compared with those for inulin. In normal rats, the plasma half-life of the elimination of oxalate was 0.33 +/- 0.06 h and that for inulin was 0.26 +/- 0.05 h (n = 10, mean +/- SD). The volume of distribution for oxalate was 56.7 +/- 6.80 and that for inulin 34.0 +/- 4.79 ml/100 g body weight, indicating that oxalate has access to additional compartments besides the extracellular volume. The total clearance of oxalate was 1.2 times higher than that for inulin. In nephrectomized rats, however, the plasma half-life of the elimination of oxalate was 1.85 +/- 0.34 h (n = 7, mean +/- SD) and that for inulin was 4.26 +/- 0.78 h. The total clearance of oxalate was 177 +/- 29 and that for inulin was 30 +/- 5 microliters/min/100 g body weight. In order to identify the extrarenal elimination route of oxalate, the bile of nephrectomized rats was collected. The hepatic clearance of oxalate was 31.2 +/- 2.7 microliters/min/100 g body weight. The biliary excretion of oxalate accounts for 17.6% of the total clearance in nephrectomized rats. Thus, other elimination processes of oxalate besides renal and hepatic clearance take place.