An inversion method, based on a genetic algorithm, is proposed for interpreting jointly various kinds of stress data in order to overcome the limitation, in number and quality, of each data set. The method has been applied to results from hydraulic tests in boreholes and to focal mechanisms of induced seismicity observed within the same depth interval. The regional stress field is described by two symmetrical tensors. The first one represents the stress at a given depth and the second one the vertical stress gradient. Results indicate that one of the principal directions is vertical. They are consistent with all but one of the hydraulic tests considered in the inversion and with about 70% of the focal mechanisms. This inversion confirms previous results suggesting that, for the scale of these induced microseismic events, the regional stress field cannot be determined solely from an inversion of the fault plane solutions. ¿ American Geophysical Union 1994