Haploids (2n = 24) of the common tetraploid (2n = 48) potato (Solanum tuberosum L.) provide promising material for attacking many problems concerned with the genetics, cytogenetics and breeding of this species. Interspecific 4x x 2x crosses between Solanum tuberosum gp. Andigena or gp. Tuberosum cultivars as pistillate parents and Solanum tuberosum gp. Phureja its source of pollen (hereafter 'pollinator') have been used to produce maternally derived haploids through parthenogenesis. This paper discusses the nature of the 'pollinator' effect in haploid extraction. The 'pollinator' had a significant effect on haploid frequencies following 4x x 2x crosses. The 'pollinator' effect seems to operate via the endosperm, in which haploid (n = 2x) embryos are associated with hexaploid endosperm. A superior 'pollinator' appears to have its effect by contributing two haploid (n) gametes to the central cell.