Currently published lithospheric strength profiles lack constraints from experimental data for shear failure of typical crustal materials in the brittle-plastic transition regime in wet environments. Conventional triaxial shear fracture experiments were conducted to determine temperature and pore pressure effects on shear fracture strength of wet and dry Tsukuba granite. Experimental conditions were 70 MPac<480 MPa, 10 MPap<300 MPa, 25 ¿C<480 ¿C, at a constant strain rate of 10-5 s-1. An empirical relation is proposed which can predict the shear strength of Tsukuba granite, within the range of experimental conditions. Mechanical pore pressure effects are incorporated in the effective stress law. Chemical effects are enhanced at temperatures above 300 ¿C. Below 300 ¿C wet and dry granite strengths are temperature insensitive and wholly within the brittle regime. Above 400 ¿C, semi-brittle effects and ductility are observed. ¿ 2001 American Geophysical Union