Abstract: An apparatus and method are disclosed for determining a maximum magnitude of bias current that can be safely applied to a head of a disc drive. The disc drive comprises a head disposed adjacent a rotatable disc having a recording surface on which data are magnetically stored, a preamplifier circuit which selectively applies bias currents to the head, and a head bias current selection circuit, operably coupled to the preamplifier circuit, which first determines the maximum magnitude of bias current that can be applied to the head in relation to a maximum power dissipation rating of the head and voltage measured across the head when at least one initial bias current of selected magnitude is applied to the head. Thereafter, a range of bias currents having different magnitudes less than or equal to the maximum magnitude are selected and evaluated to select an optimum magnitude for subsequent use by the drive.