Patients suffering from primary hyperoxaluria show elevated plasma concentrations of oxalic acid and glyoxylic acid. The in vitro absorption of these compounds onto activated charcoal, a series of neutral and ion exchange resins and onto hydrous zirconium oxide has been investigated. Hydrous zirconium oxide was the most effective sorbent studied for the removal of both oxalic acid and glyoxylic acid. In batch experiments, the zirconium oxide was capable of binding 5.5 μ mol oxalic acid and 8 μ mol glyoxylic acid per gram sorbent using 0.5 gram sorbent and 50 ml of solutions with initial concentrations of 100 μ mol.L-1 and an ionic composition resembling that of plasma. Recirculation of 2 L of the same solutions through 12 gram of mixture of hydrous zirconium oxide and alumina for 6 hours at a flow rate of 12 ml.min-1, resulted in a final concentration of 70 μ mol.L-1 of oxalic acid and 50 μ mol.L-/ of glyoxylic acid.