Polar magnetic bays are the most striking feature of magnetic records obtained by the Australian National Antarctic Research Expeditions at Macquarie Island. Negative bays are more numerous than positive bays and have greater amplitudes and durations. As a rule, negative bays commence about magnetic midnight whereas positive bays commence about 5 hr earlier. A daily reversal in direction of the bayproducing currents is indicated and the time at which this reversal takes place appears to vary with the seasons. During magnetically disturbed periods the ratio H bay amplitude to Z bay amplitude increases, indicating a northward movement of the bay-producing currents. At the same time auroras seen from Macquarie Island lie further north in the sky than usual.