OBJECTIVE--To compare HbA1c, fructosamine, and blood glucose and discuss to what degree Hba1c can be replaced by fructosamine. DESIGN--Cross-sectional study. PATIENTS--87 unselected patients coming for 112 consecutive consultations. MAIN OUTCOME MEASURES--Fructosamine, HbA1c, blood glucose. RESULTS--The following Pearson correlation coefficients were found: Blood glucose/fructosamine 0.45, HbA1c/blood glucose 0.64, and HbA1c/fructosamine 0.39. Sensitivity and specificity of fructosamine and blood glucose to detect HbA1c > or = 8.0% was shown. CONCLUSION--Our study indicates that fructosamine and fasting capillary blood glucose are poor indicators of the level of HbA1c in NIDDM patients.