The research was conducted to determinate the relationship between seed size of the sunflower (Helianthus annuus L.) and the electrical conductivity index supplied by the ASAC-1,000. This study was carried out under laboratory conditions at the ?Instituto Nacional de Semillas y Plantas de Vivero, Madrid, Espada? in 1987. The six genotypes of sunflower were classified in two categories of weight: (1) small seeded cultivars (mean weight of 100 seeds = 4-7g): Toledo-2, Peredovik and Narval SH-25, and (2) large seeded cultivars (mean weight of 100 seeds = 8-11g): Girospan-70, Toledo-8 and Monro-45. The weight variability within fenotype was determined using 100 seeds of each one of the Narval SH-25 and Toledo-8 genotvpes. The seeds were classified according their individual weight in seven classes for Narval SH-25 and for Toledo-8. The electrical conductivity index was measured in four replications of 25 seeds/tray. Seeds were soaked for twenty four hours, and a difference of voltage of 0,5v was used. The data showed that there were no significant differences among values of electrical conductivity index found for the seeds for lhe different genotypes of sunflower classified in the same class weight. However, in similarly soaked conditions, the electrical conductivity index increases as the size of the seeds is increased, where as the germinations capacity maintains almost constant.