Performance of long monolithic silica capillary columns was studied with applied pressure of up to 50 MPa.Column efficiency of 350 000 theoretical plates was observed with a 300-350 cm column of 100-200 micrometer I.D.It was possible to generate 100 000 theoretical plates with to (the column dead time) of about 5 min.Kinetic plot analysis indicated that the time required for generating the number of theoretical plates of this range with a monolithic silica column could be shorter than with a particle-packed column by a factor of about 4.Good agreement was observed between actual performance and the prediction based on the kinetic plots obtained with shorter columns.The results indicate that monolithic silica columns are well suited for such purposes.Examples of high performance separations will be shown for various samples containing polar and nonpolar compounds, which suggest practical utility of such a long column for the separation of complex mixtures.Excellent reproducibility of preparation of long monolithic silica capillary columns was observed for 100-300 cm columns prepared by several experimenters.Finally the generation of 1 000 000 theoretical plates will be reported with to of less than 200 min, and their practical utility will be discussed.