New microstructural data on experimentally deformed ''wet'' and ''dry'' natural olivine rocks (Anita Bay and ¿heim dunite), together with the other reliable experimental data, indicate that the experimental stress--recrystallized grain size relationship in olivine-rocks is largely independent of water content and temperature, and is only slightly dependent on the flow properties of the material. The experimental data cover a stress range of 30--300 MPa, water contents from <30 ppm to 300 ppm, and temperatures in the range 1100--1650¿C. Local melt contents of up to 10 volume% cannot be demonstrated to have a significant effect on the stress--grain size relationship. ¿ American Geophysical Union 1993