The present study examined the degree to which reported boredom is related to monitoring efficiency on a complex task and explored the general pattern of physiological and subjective changes associated with boredom. Forty-five male subjects performed a simulated air traffic control task for 1 hour. The subject’s task was to respond to infrequent changes in alphanumeric symbols on the simulated radar display. Physiological recordings of blood pressure, oral temperature, skin conductance, body movement, heart rate and heart rate variability, and performance measures of mean and variability of response times were obtained. In addition, subjects rated their levels of boredom, monotony, irritation, attentiveness, fatigue, and strain at the beginning and end of the session. Two extreme groups of eight subjects each were formed on the basis of their rated boredom and monotony and were compared with respect to changes in each of the measures during the task period. The two groups differed significantly on several measures with the high boredom-monotony group showing greater increases in “long response times,” heart rate variability, and strain along with a greater decrease in attentiveness. The nature of the pattern associated with boredom and monotony suggests a pattern more closely related to attentional processes than to “arousal.”