Under this type of contraceptive treatment subtle and not very striking responses were observed. An increase in fasting IRI and IRI response to glucose load, a decrease in fasting BG and no changes in NEFA or K-glucose values were the noted features. No significant weight gain was observed which could have explained the BG and IRI changes. These results are in agreement with other published data despite differences in experimental conditions. On the other hand we found a positive correlation between the IRI peaks and the number of pills ingested during the last menstrual cycle, which suggests a dose-related effect. Our data suggest that 300 μg of d-norgestrel administered postcoitally, slightly influence carbohydrate metabolism. It may be postulated that decreased insulin sensitivity by peripheral tissues leads to augmented IRI secretion in order to maintain glucose utilization at a normal rate.