Two hundred and ten healthy young women volunteered to take a combined oral contraceptive (OC) and to have glucose tolerance in insulin secretion measured in a projected 3-year study with roughly annual investigations. Although the dropout rate was high, glucose tolerance was noted to deteriorate progressively and insulin secretion to rise initially, but thereafter they remained constant. Eventually, insulin levels were lower than would have been expected from the prevailing glucose values. This combination of steroids produced marked insulin resistance to which the pancreas could respond by further insulin secretion. It is suggested that levonorgestrel is too strong a progestin for routine use in the combined OC, and it is recommended that its dose be reduced further or that weaker progestins such as norethindrone be used.