The influence of adjuvants on the efficacy of the plant growth regulators: chlormequat chloride (CCC) and prohexadione-calcium was investigated in winter wheat in 2002 and 2003. Field trials were carried out in the Agricultural Experimental Farm in Winna Góra. The plant growth regulators were applied alone at normal rate and at a r educed rate with and without adjuvants. Two adjuvants were used: Adpros 85 SL, a methylated rapeseed oil and Break-Thru S-240, an organosilicone surfactant. Crop height, lodging, yield and quality of the harvested crop were assessed. Physicochemical properties of spray solution were measured. Adjuvants improved the biological activity of both, CCC and prohexadione-calcium, especially when reduced doses were applied. Efficacy of the plant growth regulators used at normal rate without adjuvant and at reduced rates with adjuvants was similar. Break-Thru S-240 increased the efficacy of CCC and prohexadione-calcium more compared to Adpros 85 SL measured in terms of reduction of plant heigh.