The emission of dislocations from crack tips in silicon under combined conditions of temperature and stress is observed in-situ at 550 to 750°C, using transmission electron microscopy. Recording on video tape the dislocation emission and the subsequent growth of the dislocation loop away from the crack has proven to be particularly important. It has enabled the crack tip to be identified as the site of the dislocation nucleation and allows direct measurement of the dislocation velocity. Furthermore, the positions of the dislocations, required for quantitative comparison with existing dislocation models, can be measured and the extent of re-arrangement during cooling to room temperature determined. © 1989.