Magnetic recording parameters including output vs. Write current, output vs. recording density and overwrite modulation vs. Write current have been measured on eight experimental disk samples of cobalt- doped gamma iron oxide using manganese-zinc ferrite heads. Transition length parameter plus head-medium separation distance values were calculated from output vs. recording density curves. Transition length was found to increase with increasing write current and with increasing record gap length for gap lengths ranging from 0.4 to 1.25 µm. Transition lengths were also found to depend on the recording medium parameters of remanent moment, coercivity, S* and thickness. Minimum values of transition length were found to occur at write current levels insufficient to obtain adequate overwrite modulation.