Experiments were conducted on the effects of various expected noise conditions upon autonomic system activity in men during rest and work (bicycle ergometer). Skin temperature and heart rate were not appreciably, if at all, affected by any of the noises. Wide‐band, predominantly low‐frequency noise, at a level of 92 dB,A‐weighted, generally caused a decrease in pulse amplitude (indicative of constriction of peripheral blood vessels) during either work or rest, whereas an equally intense one‐third octave band of random noise, center frequency of 3150 Hz, had no appreciable effect on pulse amplitude. Repeated exposures to the wide‐band noise showed some adaptation or habituation of the pulse amplitude response during conditions of either work or rest. The results were the same for fast rise time (impulsive) bursts of wide‐band noise as for bursts with slow, gradual onsets. Rapid interruptions of wide‐band noise caused less of a decrease in average pulse amplitude than did uninterrupted noise. It is suggested that constriction of peripheral blood vessels in response to expected intense low‐frequency or wide‐band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.