SummaryHigh pressure liquid chromatography on the RPC-5 reversed-phase ion exchange system has been shown to have several potential applications as an initial high capacity step in the isolation of specific DNA restriction fragments. The fractionation of a Hinc II digest of λ DNA, which contains 35 fragments with “flush ends” ranging in size from 3 × 10⁶ to 7 × 10⁴ daltons, has been used as a model system. Under certain conditions there are some restriction fragments whose elution relative to other fragments is different on RPC-5 chromatography than it is on gel electrophoresis. In some special circumstances it is possible to obtain satisfactory yields (60–70%) of a pure restriction fragment after a single passage through an RPC-5 column.