Mechanical deformation of hexagonal close-packed (hcp) metals presents great inter-est. At low temperatures, the dominant deformation mechanism in these metals is mechanical twinning. The crystallography and core structure of twinning dislocations for the principal twin systems of hcp metals have been analysed by Serra, Bacon and Pond (1). The properties of these twinning dislocations have been investigated by atomic scale computer simulation (2), These models can be used as a reference in order to investigate the properties of hcp metals during deformation. From a geometric point of view, different behaviour is expected among distinct hcp metals. This could be attributed to the deviation of the individual c/a ratios from the ideal close-packed ratio (c/a =(8/3)1/2), which also results in the different shear moduli of hcp metals. A study of these metals is performed in order to clarify the dominance of mechanical twinning in the mechanical deformation of hcp metals, at low temperatures and various deformation rates. Results for Zn and Cd have been already published elsewhere (3,4). The twin growth in these materials is carried out through a twinning dislocation mechanism. These twinning dislocations are of an intrinsic origin and are usually arranged in parallel arrays. In this work the deformation behaviour of Ti is studied, by means of Transmission Electron Microscopy (TEM). The observations are focused in the range of 20% to 40% deformation, because under 20% mechanical twinning is negligible, whereas over 40% the vast quantity of dislocations prohibits any clear observation. For 25% deformation, a mechanism of slip transmission of dislocations through the twin is observed.