A retrospective study of 839 hospital records with various dementia diagnoses showed that 63 cases had a diagnosis of diabetes mellitus as well. None of these were found in the group of patients with senile dementia of Alzheimer type (SDAT). Oral glucose tolerance tests (OGTT) were performed in patients with SDAT, multiinfarct dementia (MID), cerebrovascular disease (CVD), hospitalized control patients (Chosp) and healthy elderly persons (Celd). Fasting blood sugar was significantly lower and the areas under the OGTT curves were significantly smaller in the SDAT group than in the CVD and the Chosp group. SDAT patients had higher insulin levels than Celd during the OGTT and on a statistically significant level 90 min after ingestion of sugar. Our findings suggest that SDAT and diabetes mellitus may not co-exist and that patients with SDAT have decreased blood sugar concentrations and elevated serum insulin levels. It is discussed whether this is an effect of the transmitter deficiencies in SDAT or may serve to explain these deficiencies.