Serum growth hormone, free fatty acids and blood glucose have been measured half-hourly for twenty-four hours in seven male patients with juvenile diabetes. Three of the patients had newly diagnosed diabetes and the four other patients had had diabetes for six to nine years. In five of the patients the studies were made during good as well as poor control. The serum growth hormone level was high and fluctuating in the newly diagnosed diabetics as well as in the diabetics with diabetes of some years duration when compared with the growth hormone level of nondiabetics. The three newly diagnosed diabetics had significantly lower diurnal serum growth hormone concentration during good control compared with poor control. In the two patients with diabetes for some years the diurnal serum growth hormone concentration was unaltered in one and higher in the other in good compared with poor control.