This paper describes a technique for selectively extracting catecholamines from body fluids prior to quantification by high-performance liquid chromatography with electrochemical detection. The technique is a two-stage process, the first stage involves the extraction of cations from the sample whilst the second stage is a liquid-liquid extraction involving the complexation of the cationic catecholamines with diphenylborate. This technique provides a very specific extraction procedure which results in chromatograms with no interfering compounds, and gives absolute recoveries of 70–80% for noradrenaline (NA), adrenaline (A) and dihydroxybenzylamine (internal standard), with similar relative recoveries of the 3 compounds. The intra-assay coefficients of variation for the measurement of catecholamines in venous plasma taken from resting subjects, are 8–9% for both NA and A, whilst the inter-assay values are 8% for NA and 20% for A.