Studies examining small groups of type 2-(NIDDM) diabetic patients have shown the potential of glucagon-like peptide 1 (GLP-1) to normalize fasting hyperglycaemia. Patient characteristics determining the size of the effect have not been reported. Therefore, the results of four studies were analysed. Exogenous GLP-1 was administered i.v. or s.c. in 37 type 2-diabetic patients, age 60 +/- 8 years; BMI 28.2 +/- 5.3 kg/m2; HbA1c 10.6 +/- 1.6%; diabetes duration 10 +/- 6 years, treatment with sulfonylureas, n = 33, metformin, n = 11, acarbose, n = 3. Results were analysed using repeated measures analysis of variance and multiple regression analysis. Exogenous GLP-1 lowered fasting plasma glucose within 4-5 h from 12.8 +/- 2.5 to 5.3 +/- 1.3 mmol/l (placebo: 12.8 +/- 2.3 to 10.0 +/- 2.2; p < 0.0001 for the interaction of treatment and time). Only fasting glycaemia (p = 0.0085) and the route (i.v. vs. s.c.; p = 0.05), but not gender, age, BMI, HbA1c, diabetes duration, treatment with sulfonylureas, metformin or acarbose, were significant predictors of the plasma glucose concentrations reached after the administration of GLP-1 (variation: 3.4-8.5 mmol/l). In conclusion, GLP-1 is able to normalize plasma glucose in all type 2-diabetic patients studied. This analysis underlines the great therapeutic potential of GLP-1.