An investigation was carried out in order to estimate the biochemical changes occurring in bitter orange (Citrus aurantium L.) leaves in response to melatonin (MEL), gibberellic acid (GA) and salicylic acid (SA) treatments. We examined the effect of MEL, GA and SA on the essential oil (EO), the total phenolic (TPC) and total flavonoid content (TFC), and the antioxidant activity of bitter orange leaves from 1-year-old plants. 15 Î¼MMEL, 1 mMSA and 1.44 mMGA increased the total leaf phenolic and flavonoid content and enhanced FRAP and DPPH activity of leaf methanolic extracts. Salicylic acid and GA promoted the leaf essential oil content and affected significantly the concentration of limonene, linalool and linalyl acetate.