A simple method for the measurement of plasma paracetamol concentrations using a novel extraction/acetylation procedure prior to gas-liquid chromatographic analysis has been developed. The sample (100 microliters) is vortex-mixed for 30 sec with 0.067 mole/l phosphate buffer, pH 7.4 (50 microliters), internal standard solution (N-butyryl-p-aminophenol (200 mg/l) in chloroform) (50 microliters) and "acetylation reagent" (acetic anhydride--N-methylimidazole (catalyst)--chloroform, 5:1:30) (20 microliters). After centrifugation at 9950 g for 3 min, a portion (5 microliters) of the resulting extract is analysed on a 1.5 m X 4 mm I.D. glass column packed with 3% (w/w) C87 hydrocarbon (Apolane-87) on Chromosorb W HP, 100-120 mesh, maintained at 235 degrees C. A specimen together with a quality control sample can be analysed, in duplicate, within 20 min. The limit of accurate measurement of the assay is 10 mg/l, and few potential sources of interference have been identified. The method has advantages of speed and reproducibility over other gas-liquid chromatographic procedures and, in addition, of selectivity over spectrophotometric techniques. The procedure provides a useful alternative to liquid chromatographic methods for emergency paracetamol measurements.