23 college students added pairs of 6-place numbers for 1, 2, 3 and 4 hrs. in random order. At 15-min. intervals they filled out subjective rating scales indicating feelings of boredom, fatigue, etc. Except for the 4 hr. period, the shorter the work period, the faster was the initial hourly rate of work. Feeling tone became progressively more unfavorable for all work periods. The rate of work during the 2, 3 and 4 hr. periods correspondingly decreased. The rate of work during the 1 hr. period was sustained.