A sensitive test is described for measuring the residual activity of 50-µm I.D. capillary columns deactivated by polysiloxane degradation. The combination of these columns with electron-capture detection is reported. A detection limit of ca. 10-15 g was found for Dieldrin, using a 4.1 m x 55 µm I.D. OV-1 column having 70,000 theoretical plates. Fast chromatograms of a test mixture of chlorinated pesticides and of Arochlor 1260 are shown, the analysis times being of the order of 10 min