It is shown that if one measures the coil current, Ic, during induction case hardening of steel a distinct break in the slope of the Ic vs. time curve is found. Experimental and theoretical results are presented which show that the break occurs at the ferromagnetic to paramagnetic transition. It is also demonstrated that in AISI 1045 steel this transition is caused wholly or in part by the crystallographic a/γ transformation. The development of the shape and depth of the case is determined experimentally and related to the Ic vs. time data. It is suggested that the sharp break in the Ic vs. time data may be utilized as a feedback signal for process control of case depths in single shot induction hardening operations.