Phenylalanine ammonia lyase (PAL) (EC 4.3.1.24) is an enzyme involved in the biosynthesis of diferent polyphenol compounds (phenylpropanoids, flavonoids etc.) andlignin in plants. PAL transcription is induced in response to various factors such as tissue wounding, pathogenic attack, light, low temperatures etc. Increase in PAL expression observed during biotic stressis asociated with triggering of defence mechanisms induced during different types of resistance – specific and systemic acquired resistance (SAR). The aim of investigation was analysis of PAL expression levels in five sunflower genotypes (two isogenic lines 393A and 393B, parental lines of Drofa F1 combination and Drofa F1 hybrid) in normal and infected with downy mildew plants grown in field. Samples were collected in field, frozen in liquid nitrogen and stored at – 80ºC. Total RNA was isolated using TRI Reagent (Ambion). First-strand cDNA was synthesized with RevertAid Reverse Transcriptase, random hexamer and oligo-dT18 primers (Fermentas) according to the manufacturer’s instructions. Expression levels of PAL were estimated by RT qPCRusing Maxima SYBR Green/ROX qPCR Master Mix (Fermentas) and Real-Time cycler DT-96 (DNA technology, Russia). The PALspecific primers were designed through Primer 3 Web v. 3.0.0. soft wareusing Helianthus annuus PAL mRNA sequence [GenBank: Y12461.1]. Obtained results showed induction of PAL expression in genotypes from Drofa F1 hybrid combination: in weakly infected – Drofa F1 and DrofaRf and susceptible, with higher levels of infection – Drofa CMS. Thus, 2,75-fold increase of PAL expression was observed in Drofa F1 medium infected plants, 3,87-fold and 3,73-fold increase in systemic and medium infected plants of Drofa CMS genotype. Isogenic lines, mostly, demonstrated decline of expression comparative with control. Only in plants from both analysed lines with systemic infection, in medium and no infected parts of weakly infected plants of 393 B line it was approximately equal with control levels. It was demonstrated that infection with downy mildew had different effects on PAL expression in isogenic lines and genotypes from DrofaF1 combination.Significant increase in PAL expression was observed in highly and medium infected plants of Drofa F1 hybrid and Drofa CMS, which indicates implication of this enzyme in defense responses in advanced stages of infection.