A procedure is described for the direct determination of zinc in human serum by fully automated, microcomputer controlled flow injection atomic absorption spectrometry (Fl-AAS). The Fl system is pumpless, using the negative pressure created by the nebuliser. It only consists of a three-way valve, programmable from the microcomputer, to control the sample volume. No pre-treatment of the samples is necessary. The limit of detection is 0.14 mg l–1, and only small amounts of serum (<150 µl) are needed for the analysis. The accuracy, as estimated by analysing sera with known amounts of zinc, is excellent, and the between batch precision is ca. 5% RSD. Peak-area measurements are used in the procedure; as a consequence the quantitation can be carried out by use of an aqueous calibration graph. The sample throughput is 40 h–1, making the procedure well suited for routine clinical analysis.