This study was conducted to explain difficulties of indirect regeneration of forest trees in tissue culture conditions. For this purpose, changes of antioxidant defense system enzymes; superoxide dismutase (SOD), peroxidase (POD) activities were determined during calli formation on young apical shoots of Abies equi-trojani (Aschers et Sinten). Young apical shoots were collected from naturally growing trees and cultured on two different media: Murashige and Skoog (MS) and McCown Woody plant medium (WPM) supplemented with growth regulators benzyl amino purine (BAP), 2,4-dichloro phenoxy acetic acid (2.4-D), kinetin (Kn) in various concentrations for callus induction. WPM media containing 1 mg ml(-1) BAP and 1 mg ml(-1) 2,4-D gave the best calli induction ratio (74 916) between tested combinations. POD and SOD enzyme activities were measured both on young shoot explants and 10 day-old calli derived from these explants. POD and SOD enzyme activities were higher, being 81.02% and 74.82%, respectively on calli when compared to shoots. The results showed that culture stress tolerated with increased antioxidant enzyme activities could be considered as protective physiological responses in calli cells.