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The tensile yield stress is compared with the uniaxial compression yield stress for specimens of polycarbonate tested at constant strain rate from -120 to + 120°C. The strain rate dependence of the tensile yield stress is also studied from - 140 to + 20°C. The yield behaviour is described by a modification of the Eyring theory of non-Newtonian viscosity where the deformation is supposed to involve two different flow processes. The validity of a yield criterion previously established by one of us, is checked throughout the range of temperatures explored; the proposed equation gives a good fit to the data provided it is applied separately to each flow process. Then the present investigation, combining the yield condition with the modified Eyring theory, provides a formalism which agrees with the data and accurately renders the temperature, strain rate and pressure dependence of the yield stress of polycarbonate. © 1972 Chapman and Hall Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published