Trimethylanilinium hydroxide was used as a derivatization agent for a broad range of phenoxy acids. Derivatization took place inside the injector immediately before gas chromatographic analysis, thereby minimizing the chance of exposing the operator to trimethylanilinium hydroxide. The reproducibility and sensitivity of the derivatization procedure were high. Maximum sensitivity for 19 phenoxy acids was 0.1-0.3 ppm. Derivatization was quantitative and did not produce by-products. The procedure required a minimum of time and effort compared with other derivatization methods in current use and is recommended for routine determinations of phenoxy acids.