Human Ss tended to choose a short, rather than a long, delay of inevitable shock; the longer the delay the less tendency there was to choose it. Over trials, preference for the 0 delay at first decreased and then increased. This U shaped curve was much less marked in the high-shock group than in the low. Ss in the low-shock group tended to choose the 0 delay on 2 or 3 trials (out of 6); but Ss in the high-shock group tended to choose it either on 5 or 6 trials, or not at all. Threatening S with an even stronger shock enhanced the tendency to choose the 0 delay. Reaction time was fairly stable throughout. GSR at the instant of shock showed no consistent pattern. (PsycINFO Database Record (c) 2006 APA, all rights reserved)