Transient temperature distributions in solid steel during common heat treatment operations have been investigated. Towards these, a mathematical model has been developed and a large number of experiments were performed in the laboratory on different grades of steel samples. Four different approaches have been considered in the mathematical model (viz., procedures based on the TTT characteristics, Fe-C equilibrium diagram, variable specific heat and negligible heat effect) to embody the heat effect (e.g., generation/dissipation) of the phase transformation reaction and to assess the associated contribution to the overall time-temperature history. Numerical predictions as well as experimental measurements appear to indicate that the procedures adopted to model the heat source/sink are not critical, as far as prediction of the transient temperature profiles are concerned.