Ability to form a conditional response to a slightly painful stimulus was tested in 10 patients before, during, and after electric shock therapy. Fifty-two experiments revealed decline in performance in 6 patients. In one the deficit disappeared within 24 hours, and in another within 2 weeks after the last seizure. Two were not tested beyond 2 weeks after treatment, and in the other 2 the impairment lasted at least 3 and 9 weeks respectively. In one of these the defect persisted through a second course of electric convulsions one month later. A seventh patient with a uniformly poor record showed an organic type deficit more definitely 2 weeks after the last seizure.This failure to adapt defensively to the experimental situation appears to be related to the number of convulsions the patient has undergone. The nature of the impairment is discussed together with some of the pertinent literature. Its essential features appear to be limitation of associative range and inability to analyze and synthetize sequentially related temporal relationships.Together with data from animal experimentation the findings suggest that important adaptive, organically determined deficits may occur more often as a result of electric convulsive treatment than are clinically recognizable.Abstract Teaser