The present paper is carried out in order to study some problems related with leaves sampling for foliar diagnosis in potato. It has been found that the fourth leaf gave good results for the soil nitrogen status at 40 and 60 days after the planting time. Both the leaflet and petiole of the fourth leaf gave good results for the soil phosphorus status. The data suggest that the diagnosis of this element in potato through the chemical analysis of the leaves must not be made very far from 40 days after the planting time. In respect to K and Ca, the data did not permit to know which part of the leaf and what age of the plant is adequate for the sampling.