In a search for rapid responses to chemical stress, uncouplers of oxidative phosphorylation and photosynthetic inhibitors were tested on nitrite and nitrate assimilation. In addition, three herbicides--Atrazine, 2,4-D and Dinoseb--were tested for their effectiveness on affecting ethylene production, dark respiration or photosynthesis. Contrary to earlier reports, the data indicated that nitrite accumulation is not an adequate measure of herbicide action. Uncouplers increased reduction of nitrate in light and darkness, whereas photosynthetic inhibitors further metabolized, irrespective of light regimen. The critical element in driving assimilation was the availability of stored carbohydrates. Because of the dynamism of the process, it is not likely that nitrite accumulation is a useful general index of herbicide activity. The marked inhibition of photosynthesis by Atrazine and Dinoseb suggested that photosynthetic inhibition might be a useful response to measure.