The effect of temperature and several metabolic inhibitors on NO3- fluxes in intact roots of 8-day-old seedlings of Pima (S-7) (Gossypium Barbadense L.) and Acala (Maxxa) (Gossypium hirsutum L.) cotton was studied. Fluxes were induced with 0.1 mM NO2- (influx) or 0.1 mM NO3- (net uptake and efflux) for 24 h. Absorption (influx and net uptake) and efflux, respectively, were determined by following NO3- depletion from, and accumulation in, the external solution. Both NO3- uptake and efflux were sensitive to temperature extremes. Net NO3- uptake decreased both at lower and higher temperatures, whereas efflux was stimulated. Azide and arsenate inhibited net NO3- uptake; however, arsenate had no effect on efflux, while azide stimulated that system. Thus, azide had a greater inhibitory effect on net uptake than on influx. Dinitrophenol also inhibited net NO3- uptake and influx and had little effect on efflux. Carbonyl-m-chlorophenyl hydrazone and diethylstilbestrol inhibited net uptake and stimulated efflux. The responses of the metabolic modifiers were similar in both Pima and Acala cotton.