A method is described for a fully automated, sensitive, accurate and precise assay for the determination of sumatriptan in human serum. The assay consists of solid-phase extraction followed by reversed-phase HPLC with electrochemical detection. The extraction procedure has been fully automated on a Zymate XP robot linked on-line to the HPLC system. The assay is linear over the analytical range 1-30 ng ml-1 and selective for sumatriptan with respect to endogenous plasma components and GR49336, the major circulating metabolite. The intra-assay data demonstrate a maximum bias and precision across the calibration range of 10% and 6.6% respectively. The inter-assay data demonstrate a maximum bias and precision across the calibration range of 6.7% and 8.8%, respectively. The extraction efficiency of the assay is approximately 90% and is constant across the calibration range. The assay was used for the determination of sumatriptan in serum clinical samples and was shown to be robust in sustained use over several months. The use of a Zymate XP robot allowed complete automation of the assay, which resulted in high-quality, high-throughput analyses.