Serum fructosamine concentrations were measured in 660 adults attending the diabetic clinic at Auckland Hospital over a 12 month period. Only 44 (6.6%) patients had results within the physiological range whereas 237 (35.9%) patients had values greater than 3.7 mmol/l consistent with poor blood glucose control. Moreover, patients with elevated frustosamine values had a much higher frequency of retinopathy than the normal fructosamine group. When frustosamine values were compared with physician's assessment of control and with random glucose results, we found weak correlations suggesting that poor control in many patients was not previously recognised. We conclude that fructosamine measurement in a diabetic clinic provides important clinical information complementing traditional assessments of metabolic control.