In the present paper, studies carried out to evaluate the effect of correction of prunning on the yield of old Niagara Rosada vines trained on unilateral horizontal cordon are reported. In a ten years old vineyard, a survey was made to check the number of spurs per plant. It was found that the number of living spurs varied from 2 to 5. In 1960, part of the plants was prunned in order to establish 6 two-bud spurs on each one. An equal number of plants was kept with the original number of spurs. The yield was recorded for ten years. The data obtained indicated that plants with 6 two-bud spurs produced 12, 26, 60 and 158 per cent more than plants with 5, 4, 3 and 2 two-bud spurs respectively.