In an earlier study (Stengel et al., 1955), reactions of various types of mental patients to eleven different painful and noxious stimuli were described. Two groups of 54 females and 43 male low-grade defectives were included in the original investigation, but it was felt at that time that the results needed further amplification before they could be usefully commented upon. In this earlier investigation only one of us actually carried out the tests, the reliability of which, therefore, was not clearly established. Furthermore, in the original testing of low-grade defectives no assessment of “Overt Reactivity” was made. As the relationship between this factor and pain reactivity in the other patient groups constituted an important finding of the study, we came to the conclusion that it would be necessary to retest some of the low-grade defective patients with these points in mind. This seemed all the more desirable as it is widely assumed that mental defectives in general, and especially low-grade mental defectives, are grossly deficient in sensitivity to pain.