Using ultra-high vacuum techniques the equilibrium pressure Pe of hydrogen dissolved in a tantalum wire has been measured over the pressure-temerature-concentration ranges 10–7–10–2 torr (1 torr = 133.32 N m–2), 311–484 K and 0.19–3.33 atomic %(or 0.0019–0.0333 H/Ta atomic ratio) respectively. Ideal solution behaviour was observed for hydrogen concentrations below about 2.6 atomic % described by the expression C=√Pe(2.4±0.1)× 10–3 exp [(4.3±0.1)× 103/T], where C is in atomic %, Pe is in torr, and T is the temperature in K. The relative partial molar heat of solution ΔH° is –(36.0 ± 0.8)× 103 J g-atom–1 and the relative partial molar entropy, ΔS°, is –(50 ± 2) J deg.–1 g-atom–1. The rate of evolution of hydrogen dissolved in a tantalum wire in a continuosly pumped vacuum system was also studied over the pressure and temperature ranges 10–4–10–7 torr and 396–513 K respectively. The rate-limiting process was identified as the recombination of H atoms at the metal surface rather than diffusion in the metal bulk. The activation energy for this process is –(33.0 ± 1.5)× 103 J g-atom–1.