Insulin release is a complex oscillatory process with rapid pulses (10 min) superimposed on slower circhoral oscillations (50–100 min). The exact mechanism of the circhoral oscillations, which are probably in part the consequence of a negative feedback loop linking glucose and insulin secretion rate, remains unclear. Stimulatory effects of sleep on insulin secretion are achieved by an enhancement of the oscillation amplitude which could be partly mediated by GH. The different patterns observed after acute or chronic shift of sleep suggest however an interaction between sleep influence and circadian rhythmicity, as described for numerous pituitary hormones. The intra-sleep awakenings have a modulatory effect on glucose levels but no systematic relationship exists between glucose or insulin secretion rate oscillations and the REM-NREM sleep cycles. Irrespective of the mechanisms involved, sleep or GH stimulatory effects result from a modulation of the oscillation amplitude rather than of their frequency which is probably an important feature of insulin efficacy.