To assess the dynamics of taurine metabolism in vivo, 2 sets of studies were carried out in healthy volunteers. First, pilot studies were carried in a single human subject to determine the time course of plasma and whole blood isotope enrichment over the course of an 8-h, unprimed continuous infusion of [1,2-¹³C₂] taurine. Secondly, 5 healthy adult males received two tracer infusions on separate days, and in randomized order : (i) a 6-h, continuous infusion of [1,2-¹³C₂] taurine (3.1 ± 0.2 µmol.kg^-1.h^-1) and (ii) a bolus injection of [1,2-¹³C₂] taurine (3.0 ± 0.1 µmol.kg^-1). Isotope enrichments in plasma and whole blood taurine were determined by gas chromatography-mass spectrometry. The pilot experiments allowed us to establish that steady state isotope enrichment was reached in plasma and whole blood by the 5^th hour of tracer infusion. The plateau enrichment reached in whole blood was lower than that obtained in plasma taurine (p<0.02). In the second set of studies, the appearance rate (Ra) of plasma taurine, determined from continuous infusion studies was 31.8 ± 3.1 µmol.kg^-1.h^-1 . After a bolus injection of tracer, the enrichment decay over the subsequent 2 hrs was best fitted by a two-exponential curve. Taurine Ra was ~85% higher when determined using the bolus injection technique, compared with continuous infusion of tracer. We conclude that : 1) taurine appearance rate into plasma is very low in healthy postabsorptive humans, and --due to taurine compartmentation between the extra and intracellular milieus-- may only represent interorgan taurine transfer, and merely a small fraction of whole body taurine turnover; and 2) the bolus injection technique may overestimate taurine appearance into plasma. Further studies would be warranted to determine whether alterations in bile taurine dynamics affect taurine Ra.