Hydrogen peroxide and other atmospheric trace gases were measured along the 91¿30' meridian from near the Iowa border to the Gulf of Mexico during February 1987. The measured H2O2 values were within the range of <0.1 to 1.0 ppbv and an increase in concentration from north to south of 0.04--0.05 ppbv per degree of latitude was observed on five of six flights. The concentration of H2O2 appeared to be primarily dependent upon air mass boundaries. H2O2 measurements during flights in air masses of similar histories during daylight and night showed no significant difference in concentration. Neither was there a consistent dependence of the H2O2 concentration upon altitude.