A comparative serological and psychological investigation was conducted of 52 institutionalized cases of dementia paralytica. In general, it was found that the treated cases with negative spinal fluid showed a more pronounced deficit both of intelligence and of personality resources than those cases still in an active phase. There was evidence, on the one hand, that part of the impairment to psychological functioning is reversible when the disease process is arrested early in the psychotic stage and, on the other hand, that some of the cases may continue to deteriorate even though treatment has rendered their spinal fluid negative. To explain these 2 opposite trends it would seem necessary to consider that there are at least 2 pathogenetic factors of general paresis. As judged from the test results, the psychological deficit found in dementia paralytica appears to differ from that of senile dementia.