With the increase in the aged population, it is expected that the number of debilitated aged people will increase and that the number of patients receiving many medications will increase. However, there have been few reports of clinical pharmacological studies on blood pharmacokinetics, metabolism, adverse effects, etc, of drugs used in debilitated aged people who have lowered physical and mental functions complicated by many diseases. Thus, for the large part, pharmacokinetics in these patients remains unelucidated. We experienced eight cases of marked hypoglycemia of unknown cause in patients who had not taken any hypoglycemic drugs or insulin and examined the relationships between the event and the physical features and medications of the patients. The eight patients included both males and females aged 66 to 88 years (mean: 78.5 years). The eight patients were all aged and showed cerebral infarction, reduced volition, etc. The onset of hypoglycemia was preceded by decreased appetite and an abrupt manifestation of severely disturbed consciousness a few days previously. Laboratory tests revealed marked hypoglycemia in 8 cases, leucocytosis in 7 cases (not examined in one case), metabolic acidosis in 3 cases, elevated GOT in 5 cases, elevated GPT in 2 cases, increased BUN in 1 case, and positive CRP in 4 cases. The patients had been taking an agent to activate brain metabolism/improve mental symptoms (Hopantene calcium: 7 cases; Idebenone: 1 case). The Idebenone-treated patient had received Hopantene calcium for eleven months prior to receiving Idebenone. Furthermore, the findings resembled those of Reye's syndrome often noted in children.(ABSTRACT TRUNCATED AT 250 WORDS)