Paleostress magnitudes can be estimated by using fault slip data, rupture and friction laws (Angelier, 1989) for dry conditions. However, their estimation is difficult if fluids are present during deformation, the lithostatic load and the fluid pressure being generally unknown. This paper shows that the quantitative estimation of the lithostatic load and the fluid pressure during a tectonic event can be derived from paleofluid analysis in fluid inclusion planes, (FIP). As FIP are healed mode I cracks oriented in a consistant manner relative to regional or local structures, stress and fluid features may be obtained for a given deformation event. This approach has been applied to a fault system affecting an Hercynian granite of the NW French Massif Central. A NW-SE compression has been defined from a population of 51 faults characterized by orientations around N60 ¿E to N110 ¿E for dextral strike slips and N135 ¿E to N175 ¿E for sinistral movements. The stress ratio has been determined with fault slip data around 0.52¿0.08 and by using Angelier's method, the ratio &PSgr; (&sgr;3/&sgr;1) was estimated around 0.27¿0.03, and the friction coefficient μ was estimated around 0.58¿0.1. FIP orientation were measured in a sample collected at 1 meter from the fault. The dominant trend is NW-SE, vertical or dipping toward the SW. Inclusion fluids from FIP are characterized by homogenization temperatures in the 260¿--380 ¿C range with a mode around 300 ¿C and melting temperatures from 0 ¿C to -1.5 ¿C (0--5% equivalent NaCl) with a mode around -1.0 ¿C (1.7% equivalent NaCl). These data yield, assuming a geothermal gradient in the 60¿--80 ¿C/km range, and hydrostatic conditions, a fluid pressure estimate of about 50¿10 MPa and a &sgr;V around 132¿10 MPa. Thus a major stress ratio &sgr;1--&sgr;3 can be estimated in the 70--105 MPa range. ¿ American Geophysical Union 1995