Rats received shock that was predicted by cither a light signal alone, light-tone complex signal or no signal. In the light signal alone and light-tone complex signal conditions, experimental rats which could avoid and/or escape shock developed less gastric ulceration than did yoked “ helpless “ rats which had exactly the same shock but had no control over shock. In the non-signal condition, ... [Show full abstract] however, the experimental rats did not differ from the matched yoked rats. Ulceration of non-shock control rats was negligible as compared to experimental and yoked rats in each of the three warning conditions. Presence or absence of a safety signal has an effect on ulcerogenesis. The light signal alone condition was effective in reducing ulceration for “ helpless “ rats as well as rats which could control shock. Thus, the effectiveness of a coping behavior depends on the reliable prediction of shock in a stressful situation. © 1983, The Japanese Psychological Association. All rights reserved.