A medium-frequency (0.1-1.5 MHz) mutual-impedance probe was flown on three rockets in the auroral ionosphere, for the purpose of measuring the field-aligned drift velocity of the thermal electrons. Detailed results are presented from one of these experiments, in which a sensitivity of the order of 1% of the electron thermal velocity was achieved. Downward electron drifts were indicated, but their high apparent velocities cast doubt on their authenticity. Data from this and the other two experiments suggest that the probe was being perturbed by the payload body. This problem needs to be solved, and the sensitivity improved by an order of magnitude, in order for the probe to become a useful measuring instrument.