When deformation leads to differential movement along interfaces—for example faulting, flexural slip folding, grain-boundary slip—heat is generated by friction. Opinions differ concerning the importance of mechanically generated heat during regional dynamothermal metamorphism. Turner and Verhoogen (1960) deferred a definite conclusion until such time as quantitative data might become available. A mathematical solution to the non-steady-state heat flow problem permits the calculation of temperature rise in response to a given rate of heat production within a bounded region in the crust. This solution may find application in specific cases, provided the variables can be evaluated reasonably precisely. The computations presented here of temperature increases at eight depths for each of.40 models show that frictional generation of heat may result in significant local elevation of temperature. Variables used in the computations are: time and rate of heat generation, and depths of boundaries within which hear is generated. Average energy per gram converted to heat and strain rate within the deforming part of the crust are computed for each model. Frictional heat due to deformation is not solely responsible for the temperatures of regional metamorphism but may, when deformation is concentrated in space and time, account for local steepening of the temperature gradient, and locally for a mineral assemblage of higher metamorphic grade than would otherwise have been present.