Oscillations were detected in the time course of both blood glucose (B.G.) and serum immunoreactive insulin (I.R.I.) after oral administration of 50 g of glucose in twelve normal subjects. There was a considerable variation in the time periods of oscillation over the group studied Despite this there was a high degree of intra-subject correlation in the time periods of B.G. and I.R.I. oscillation. There was a general in-phase relation between the oscillatory time courses of the two parameters with a dispersion increasing with successive extremes of oscillation. These oscillations are interpreted as a consequence of under damped short-term feedback regulation of blood glucose. The in-phase relationship between B.G. and I.R.I. is consistent with a rapidly releasing component in the glucose stimulus to insulin release, and with the early release of insulin by enteric hormones. It is postulated that secondary and tertiary peaks in blood glucose may represent a redistribution of glucose after initial hepatic deposition. 1 Supported by National Health and Medical Research Council, Australia