At 3 sites in South Australia daminozide reduced mean potato tuber weight by 9-13% (P<0.05). Total yield of potatoes was reduced by 6-11%, although the effect was significant (P< 0.01) at only 1 site (Purnong Landing, reduction 11%). There were no effects of daminozide on tuber number, uniformity of tuber weight, specific gravity of tubers (at 1 site) or yield of ware grade tubers (80-350 g fresh weight). However, daminozide increased yield of grades (90-130 g) by 40% and decreased yield of grades (260-350 g) by 32% (P<0.05). In achieving these results, rates of 0.85, 1.7, 3.4 and 6.8 kg a.i. ha-l of daminozide were about equally effective. We conclude that, unless there is a market requirement for tubers of 90-130 g in weight, daminozide should not be used for the cultivars Sebago, Exton and Coliban if haulms are killed by herbicide or disease from 15 to 30 days before natural plant senescence. Stem length and leaf area index were reduced early in the season by daminozide, but late in the season leaf area index was increased.