This study aims at explaining the absence of a threshold for crack propagation in an α/β titanium alloy during cyclic tests performed with constant Kmax and increasing Kmin, if Kmax is higher than 60–70% of KIc. Tensile, creep as well as fatigue crack growth tests are performed on specimens with various hydrogen content. SIMS analyses of hydrogen content around the tip of a crack developed in the abnormal regime are made. Solute hydrogen is shown to segregate at the crack tip and to enhance room-temperature creep, strain localisation and decohesion along α/β interfaces.