[en] The ion temperature gradient (ITG) driven instability is investigated for a plasma with trapped ions and collisions. For the toroidal branch, the perpendicular temperature gradient is needed for the instability in contrast to the slab branch. The threshold value of the temperature gradient is higher with trapped ions and is further increased by electron and ion collisions. A theoretical model is used to explain the experimental results for a hybrid trapped ion ITG mode in the Columbia linear machine. (author). 19 refs, 4 figs