The effect of IAA, GA3 and kinetin applied three times per season as a foliar spray on the yield of barley (Hordeum vulgare L.) Cvs. Piast and Bomi was studied in a greenhouse experiment. IAA inhibited tillering and decreased the grain mass in ‘Piast’ and reduced the straw
mass in Bomi, but increased the kernel number per plant in ‘Piast’ and the kernel number of the main stem ear in Bomi. GA3 increased tillering and the straw mass in both cultivars and kinetin in Bomi cv. IAA and kinetin increased the grain mass per plant in this cultivar. GA3 reduced the grain mass and kernel number per plant in both cultivars and decreased the harvest index but increased 1000 grain weight.