The effects of ethyl alcohol (1 ml/kg body weight), dextroamphetamine (15 mg), and nitrous oxide (20%) on reaction time were investigated in 6 subjects with a 2-, 3-, and 4-choice serial reaction time task. Each drug was assessed separately and in combination with nitrous oxide. The error rate was held constant. Neither ethanol and nitrous oxide nor amphetamine and nitrous oxide influenced the slope of the Hick-Hyman function, but the former combination increased the intercept while the latter decreased it. The drugs, either alone or in combination, shifted the frequency distributions of the reaction times as a whole, rather than modifying either their shapes or the pattern of the response latencies around an error. These results indicate that the drugs have a common pattern of effects on reaction time and that alcohol exacerbates narcosis while amphetamine ameliorates it. This is interpreted as support for the view that narcosis causes a nonspecific slowing of information processing by decreasing arousal.