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Potatoes (Solanum tuberosum cv. Sebago) were grown near Melbourne on a duplex soil during November-May under 3 irrigation schedules: TI, wet (irrigated every 5-9 days); T2, medium (irrigated every 12-1 7 days); and T3, dry (irrigated every 36 days). Root distribution was studied for the plants from the tuber setting stage in January, through flowering to tuber bulking in March; root growth was different in all treatments, significantly (P < 0.05) so on some occasions. The wet treatment T1 had more deep roots early in the growing season (January) than did the drier treatments but, by late February, root length was greatest in the driest treatment. During the latter part of February and March total root length per unit ground area diminished in all treatments, but the reduction was less in the drier treatments (T2 and T3). Root length densities ranged from 7.5 to 40 km/m3. Leaf area index of the crop in T1 was always significantly greater than those of T2 and T3. Between late December and late March the average daily water use for the crop was 5.4, 3.7 and 2.2 mm day-1 for TI, T2 and T3 respectively and, from these data, the relative evapotranspiration rates were calculated as 0.94, 0.66 and 0.38 respectively. Yields of tubers, harvested in May 1983, from T2 and T3, were at least 60% less on a fresh weight basis than from T1. Tuber water percentage at harvest was not affected by different irrigation treatments. Water use efficiency was slightly greater for T1 than for T2 and T3. We conclude that, on this soil, frequent light irrigations are necessary to obtain high yields of potatoes, but care must be taken because of the potential problem of a perched water table.