The transplanters of grafted vines at present on the market are equipped with laser transmitters and receivers, which ensure the parallelism among the vineyard rows. These high cost instruments cause some operational problems: not operational return way of the machine, the need for more than one surveyed point when the soil shape is irregularar, the need of two operators, besides the machine driver, etc. The aim of this work is to assess the accuracy of GPS systems in order to use them in place of the laser systems. The distances among the grafted vines and the distances among the vineyard rows were measured using two positioning systems (a differentially corrected GPS system - DGPS) and a low cost GOS receiver) in a previously mechanically transplanted vineyard. The results showed that these systems can substitute efficiently the laser systems. However a study about their economical convenience is neeeded.