In 161 consecutive cases of fluctuant hearing loss and 13 control cases of other causes of deafness, patients were examined for their ability to metabolize a 100 gm. oral dose of glucose. 2. The plasma glucose level in response to the oral dose of glucose was measured at hourly intervals for three hours. 3. Insulin and proinsulin levels were measured in 46 cases of fluctuant hearing loss and in 13 control cases. 4. None of the control group showed borderline or diabetic tolerance curves. 5. Fourteen per cent of the patients with fluctuant hearing loss had borderline glucose intolerance curves and 19 per cent showed diabetic glucose tolerance curves. 6. In patients whose insulin and proinsulin levels were determined, the insulin response to an oral glucose load was typical of adult onset diabetes, i.e., delayed hyperinsulinemia with concomitant hyperglycemia. The hyperinsulinemia was not associated with hyperproinsulinemia. 7. We conclude that in patients with fluctuant hearing loss there is a significantly higher incidence of borderline or diabetic glucose tolerance than in the "control deafness" or "normal population" group.
