To determine whether the dawn phenomenon occurs in healthy elderly subjects, we compared glucose and insulin levels as well as glucose production rates in 10 young nondiabetic men (mean age 26 +/- 3 years) and 10 old nondiabetic men (mean age 69 +/- 3 years) between 0500 to 0800. Young subjects demonstrated a modest but significant rise in plasma glucose level (89 +/- 1 mg/dl to 92 +/- 1 mg/dl, p less than .05) and glucose production rate (1.7 +/- 0.1 mg/kg/min to 1.9 +/- 0.2 mg/kg/min, p less than .05) between 0540 and 0800. No rise was detected in the plasma glucose or glucose production rate in older subjects as a group, between these times. However, a few elderly subjects did display a dawn glucose rise. Changes in plasma insulin levels were not significant for either young or old subjects. Older subjects had significantly lower mean peak growth hormone levels during the night than young subjects (6.7 +/- 1.3 vs 10.1 +/- 1.6 ng/ml, p less than .05). These results demonstrate a modest rise in plasma glucose levels and glucose production rate in healthy young subjects consistent with previous reports of the dawn phenomenon. This modest early morning glucose rise is absent in most otherwise healthy older subjects.