This experiment was conducted to determine whether NO2 influences the effects of SO2 on growth of two legumes (barrel medic and lucerne). Plants were exposed to <5, 55, 149 or 262 nl l-1 of SO2, and <5 or 170 nl l- of NO2 for 4 hr day-1 for 108 days in a factorial experiment using outdoor open-top chambers. NO2 halved shoot dry weight and had smaller effects on stem length and shoot nitrogen concentration in both species. SO2 significantly decreased shoot weight and stem length at the higher concentrations. In addition, mixtures of NO2 and moderate SO2 concentrations had more severe effects on growth parameters than either SO2 or NO2 alone, and exceeded the sum of their independent effects.