Fruits from three walnut cultivars were picked in three terms with the aim to determine the optimal harvesting time of green walnut fruits for the improvement fruit brandies. Quantity of juglone and its antioxidant activity was determined in the picked fruits. Juglone quantity was the highest in fruits weighing between 4.5 g and 6.5 g (harvesting time around June 1), and varied from 209.60 mg up to 735.00 mg in the cultivar Sheinovo, from 388.50 mg up to 418.60 mg in the cultivar Geisenheim 139 and from 325.50 mg up to 499.40 mg in the cultivar Geisenheim 251, in a sample of 100 fruits. In this phase, walnut fruits had the highest antioxidant activity, too. .Tehnikom visokoefikasne tečne hromatografije određivan je sadržaj juglona (5-hidroxi-1,4-naftohinona) u uzorcima mladog oraha različitih sorti i različite zrelosti berbi 2005. i 2006. godine. Pored toga određena je anatioksidativna aktivnost metanolnih ekstrakata uzoraka plodova. Koncentracije juglona se nalaze u opsegu 0,03-0,24 % za berbu 2005. i 0,03-0,08 % za berbu 2006. Svi uzorci su pokazali značajnu antioksidativnu aktivnost.
