Injection on capillary columns without stream splitting has generally been understood to be a special application of cold trapping. As far as liquid samples are concerned, this is not so, as the method also works isothermally, i.e., with injection and elution at the same temperature. In the first phase of the analysis, the large amount of solvent prevents migration of sample components, thus concentrating their vapour plugs to 1% or less of their original length. The solvent should therefore be considered as an important parameter in the analysis, instead of being eliminated by means of complex additional equipment. In order to exert its full effect, the solvent has to be sufficiently retained by the column. The dependence of the effect on solvent volatility, column temperature, polarity and some instrumental conditions is discussed.