Fertilization may help crops to yield better. To determine whether mete orological and soil conditions influence the productive response of nitrogen fer tilization in sunflower, a study was conducted in an Italian interregional project (BIOLI). The effects of nitrogen fertilization on two commercial high oleic varieties (Carnia and PR 64 H 61) was investigated in North East (Udine) and East Central Italy (Osimo) during 2005. Nitrogen fertilization was not effective in Osimo under rainfed and drought conditions, whereas the highest N level gave the best yield in Udine in wet and irrigated conditions. In both locations plant size was positively influenced by fertilization. No differences were observed among varieties in Osimo, whereas in Udine the locally selected hybrid had the best performance. Nitrogen fertilization is suggested only in good weather conditions and in nitrogen poor soil. Under drought conditions nitrogen influences plant growth but not yield.