The chronic hyperglycemia of non-insulin-dependent diabetes mellitus (NIDDM) evolves gradually and is usually preceded by more transient hyperglycemia, classified as impaired glucose tolerance (IGT). Already in this phase, there is an increased risk of cardiovascular complications, and many IGT subjects, like NIDDM patients, often display several of the metabolic and circulatory disturbances that are associated with hyperglycemia, e.g., insulin resistance, hyperinsulinemia and/or hyperproinsulinemia, delayed insulin release, dyslipidemia, and hypertension. Therefore, and because untreated hyperglycemia is a self-perpetuating condition, early detection and early intervention may be necessary to prevent the progression and complications of NIDDM. This in turn would necessitate screening procedures, and the therapeutic goal should include both euglycemia and normalization of plasma insulin, plasma lipids, and blood pressure. A study in the German Democratic Republic indicated that the mortality in screening-detected NIDDM patients did not differ from that in patients detected in routine care. In a Swedish study on screening-detected NIDDM subjects, only those who had IGT rather than manifest NIDDM could maintain fasting blood glucose less than or equal to 6 mM for 5 yr by hypocaloric dietary regulation alone. In those with screening-detected NIDDM, the delayed acute insulin release and net postprandial hyperglycemia were improved by addition of glipizide, and most managed to attain and maintain fasting blood glucose less than or equal to 6 mM for approximately 2 yr after such addition. However, after 4 yr, there was an increase in blood glucose, suggesting that preventive intervention either may not be possible or may have to start in the IGT phase.(ABSTRACT TRUNCATED AT 250 WORDS)