The mechanical properties of H11 and AISI 4350 steels were determined for a series of bainites formed from both deformed and undeformed austenites. These bainites were also subjected to subsequent straining and tempering treatments. Similar thermomechanical treatments involving martensite as the essential transformation product were included for comparison purposes. Fifty per cent austenite deformation in H11 results in considerable strengthening of the subsequently formed bainite. H11 in the bainitic condition, formed from either deformed or undeformed austenite, is strongly affected by refrigeration in liquid nitrogen, owing to conversion of retained austenite when tempering temperatures below 1000 F are employed. In both cases, a large secondary strengthening is observed on tempering between 1000 and 1100 F. This results in higher strengths and equivalent ductilities as compared to the correspondingly treated martensites. Austenite deformation in 4350 has little effect on the strength of the subsequently formed bainite, although such deformation does enhance the strength of martensite. H11 and 4350 bainites and martensites exhibit a large response to strain-tempering treatments. For both steels, small deformations (up to 3 per cent) produce large strengthening effects. Yield strengths close to 400,000 psi have been obtained by the application of strain-tempering treatments (50 per cent deformation) to both H11 martensite and bainite. Increasing the carbon content in 43XX steels enhances the strengthening response to strain-tempering. The increments in strength developed by deformation processes, both before and after transformation to either bainite or martensite, are found to be approximately additive when the individual processes are combined.