In three experiments a total of 100 hungry rats were trained to run an alley for food reward and then given electric shocks at the goal to induce an approach-avoidance conflict. These experiments yielded the following results and conclusions:
1. During all but the first one or two trials of an extended test series with strong electric shocks at the goal, Ss which previously had been habituated to a gradually increasing series of shocks at the goal performed markedly better than those suddenly exposed to the test shocks for the first time. Under the conditions of these experiments we were able to teach rats considerable resistance to the stress of quite strong electric shocks at the goal.
2. A similar gradually increasing series of shocks given outside of the rewarded conflict situation produced little, if any, effect; Ss receiving this treatment were similar to the nonshock controls and reliably poorer than those habituated to the shocks in the rewarded training situation. Apparently, mere exposure to tough treatment will not necessarily improve resistance to stress in a different criterion situation.
3. Contrary to original expectation, additional rewarded training trials given to Ss which had reached the asymptote of speed reduced, rather than increased, the resistance of their running habit to disruption by shocks at the goal. Although widely advocated, mere overtraining may not always be helpful preparation for subsequent stress.

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