A method of measuring the hydraulic conductivity of compacted clay liners in the field using single-ring infiltrometers has been developed. It is assumed that the ring has a diameter that is no less than the thickness of the clay liner and that the clay liner is underlain by a freely draining material with negligible suction. Finite element analyses were performed to develop correction factors that account for horizontal seepage for cases in which the ring infiltrometer is partially embedded into the liner. The correction factors were developed for a range in diameter of the ring and for ratios of horizontal to vertical hydraulic conductivity of 1, 10, and 100. Laboratory experiments were conducted to verify the results of finite-element analyses, but the laboratory results showed considerable scatter and were successful only in demonstrating that the finite-element results show the proper trends. Finally, the test method was tried in the field on a full-sized clay liner in which the actual hydraulic conductivity of the entire liner could be calculated from the known rate of leakage. The hydraulic conductivity measured in the infiltration test agreed almost perfectly with the computed overall hydraulic conductivity of the entire liner. It is concluded that the single-ring infiltration test can be used to measure the hydraulic conductivity of clay liners, although it is difficult to measure hydraulic conductivities that are substantially lower than 1 × 10−7 cm/s. In addition, the field tests may take several weeks to complete.