A microcalorimetric method is proposed to determine the contact angle of a nonwetting liquid within a mesoporous solid. It is based on the simultaneous measurement of the heat and work of wetting,as the pressure is raised. The method simply requires a previous determination of the surface area to be wetted. It allows one to carry out liquid intrusion porosimetry without any a priori assumption on the contact angle. This method is, in principle, applicable to mercury porosimetry. Its feasibility is shown here for water in porous hydrophobic silicas.