AbstractThis report describes an on‐line capillary GC injection system which enables on‐column injection of a hundred or more microliters, and yields separations comparable with those obtained from on‐column injection of 1–2 microliters of solutions a hundred times more concentrated. Precision, carry‐over, linearity, and discrimination are comparable with those of classical sample‐introduction techniques. A selection of polar and high boiling compounds has been examined, and excellent peak shapes obtained for hundreds of injections. Initial results indicate that maintenance and long‐term reproducibility will also be comparable with those of classical techniques.The instrument utilizes a version of the large volume on‐column injector with solvent diversion described in an earlier communication, with the addition of a method for independent heating of the retention gap. This modification reduces the effects of activity in the retention gap and improves the capability of the technology to handle complex mixtures. It also increases reliability and system lifetime, fits readily into most GC ovens, is easily automated, and should be compatible with all capilla