Pollinisers of the sweet cherry cultivars ‘Stella’ and ‘Summit’ were determined by analysing isozymes of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6-PGD), glucose phosphate isomerase (GPI), isocitrate dehydrogenase (IDH), shikimate dehydrogenase (SKDH), fructose-1,6-diphosphatase (FDP), and glutamate oxaloacetate transaminase (GOT) in their embryos. Possible polliniser cultivars were selected on the basis of similar full bloom dates and orchard position in regard to Stella or Summit. Examination of the ratios for the segregation of isozymes showed that Summit was predominantly pollinated by Stella, and Stella by Van. In the same orchard, but in a different season, the main polliniser for Stella was found to be Venus, and 29% of Stella embryos resulted from selfing. Thus the effectiveness of cherry pollinisers depends on overlapping flowering dates, which can vary from year to year, and, for a self-fertile cultivar in a mixed block, cross-pollination predominates over selfing.