Experiments were carried out to determine the effect of certain variables on rats'' preference for signal-shock vs. shock-signal. 136 Ss [subjects] were run daily for 11-hr. periods during which they received unavoidable shock at predetermined intervals. When S was in one end of the experimental box the shock was preceded by a signal (light), in the other, S received shock-signal. The most marked preference for signal-shock was obtained with a 500-v. shock delivered 12-60 times per hour using a shock of .5- or 5-sec. duration and an 18-sec. signal. Significantly less time was spent on the signal-shock side with a decrease in signal duration to 3 or .5 sec. or a decrease in shock frequency to 2 per hour. A reversal of side preference followed a reversal in the sequence of signal and shock. A significant preference for signal-shock was obtained even when shock was delivered through ear clips in such a way that S''s responses could not affect the part of S''s body in contact with the electrodes.