Stress corrosion cracking (SCC) susceptibility of some h.c.p. metals: titanium, zirconium and one of its alloys, Zircaloy-4, was investigated in iodine-methanol solutions. Slow strain rate tests were carried out until the rupture of the specimens, in some cases interrupted strain rate tests were conducted. SCC was observed in all the systems studied, but preceding crack propagation, intergranular attack was found in all cases, and this intergranular attack was due to anodic dissolution of the grain boundaries. The rate controlling step is the diffusion of iodine to the tip of the advanced crack. It was also demonstrated, that it is necessary to locally disrupt the passive film to induce SCC in these materials and this is done by the chemical effect of the iodine molecules on both, titanium and zirconium oxide film. Once the intergranular attack reaches a certain value, a transition to a transgranular cracking mode occurs. This last step was identified as the true SCC process. The surface-mobility SCC mechanism was applied to explain the results obtained.