Leaf samples of 55 pistachio (Pistacia vera L.) cultivars from 13 countries were analysed using horizontal starch gel electrophoresis to study isoenzymatic variability for seven isoenzyme systems: aconitase (ACO), esterase (EST), glutamate oxalacetate transaminase (GOT), glucose phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM) and shikimate dehydrogenase (SKD). Polymorphism was observed in five of them (ACO, EST, GPI, PGM and SKD). GPI showing 8 different phenotypes was the most useful for the characterization of cultivars. Twelve different combinations for female cultivars and 2 for male cultivars were found. Two female cultivars ('Bianca' and 'Red Jalap') and 4 male types ('A', 'C-Especial', 'M-P3' and 'M-P9') were identified as being of hybrid origin. No pattern of geographic distribution of isozyme variation in this species was observed.