Oxime derivatives (methoxime, benzyloxime, trimethylsilyloxime) of 17-ketosteroids will, under some gas chromatographic conditions, undergo Beckmann fission in the injector zone. The result of this effect is partial or total conversion of the steroid derivative to a nitrile. Since oxime derivatives are widely used in gas chromatography for steroids and other compounds, it is important to recognize that this reaction may occur. In analytical separations conditions which do not lead to the fission reaction should be maintained.