Field experiments designed to determine the efficacy and interaction of hexazinone [(3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] and nitrogen on weeds and lowbush blueberry [Vaccinium angustifolium (Ait.)] growth and yield were established at five locations in 1980 and 13 locations in 1981. Hexazinone was applied after pruning, preemergence with nitrogen, using a split-block design, with locations serving as replications. Grasses, goldenrod (Solidago spp.), and meadowsweet [Spiraea latifolia (Ait.) Borkh. # SPVLF] were reduced significantly as the rate of hexazinone was increased. Blueberry injury, plant stand, number of flower buds, and yield all increased with increases in hexazinone rate. Variations in blueberry yields occurred among locations due to differences in plant stand and productivity, as well as climatic and edaphic factors. Within each nitrogen rate, increases in the rate of hexazinone resulted in a quadratic increase in blueberry yield. Within the hexazinone treatments, increasing nitrogen had no effect on yield. Blueberry yield reached a maximum of 3926 kg/ha at a hexazinone rate of 1.83 kg/ha. Partial budgeting was used to evaluate the effect of combinations of hexazinone and nitrogen on net income. Response function analysis determined yield and profit-maximizing combinations of hexazinone and nitrogen. Partial budgeting indicated that hexazinone alone or combined with nitrogen increased net income, but nitrogen without hexazinone decreased net income. Response function analysis indicated that hexazinone at 1.79 kg/ha without nitrogen maximized profits.