Glomerular filtration rate, kidney volume, and urinary albumin excretion rate were studied in otherwise healthy newly diagnosed Type 2 (non-insulin-dependent) diabetic patients, untreated at diagnosis, after short-term treatment and after 3 months treatment. In 10 patients (Group A) glomerular filtration rate (measured by the plasma clearance of 51-Cr-EDTA) decreased from the time of diagnosis 106.2 +/- 14.6 ml.min-1.1.73 m2(-1) (mean +/- SD) to 95.9 +/- 13.7 ml.min-1.1.73 m2(-1) after 3 months treatment (p = 0.049). At the same time, mean plasma glucose was reduced from 13.3 +/- 3.2 mmol/l to 6.5 +/- 1.1 mmol/l. The fall in mean plasma glucose was correlated to the reduction in glomerular filtration rate, r = 0.76, p = 0.011. Kidney volume as measured by ultrasonic scanning was reduced from 264.0 +/- 33.7 ml/1.73 m2 to 210.8 +/- 23.8 ml/1.73 m2 (p less than 0.005). The relative decline in urinary albumin excretion rate was correlated to the fall in glomerular filtration rate, r = 0.69, p = 0.026. In 15 patients (Group B) 24-h urine collections were made during 9.5 +/- 3.2 days, urinary albumin excretion rate fell from the first to the last day in hospital from 14.0 x/divided by 3.0 micrograms/min (geometric mean x /divided by tolerance factor) to 7.0 x/divided by 2.7 micrograms/min p = 0.015. The relative decline was correlated to the change in mean plasma glucose, r = 0.65, p = 0.032. Thus, kidney function in Type 2 diabetic patients is influenced by metabolic control, although to a lesser extent than is seen in Type 1 (insulin-dependent) diabetic patients with comparable glycaemic control.(ABSTRACT TRUNCATED AT 250 WORDS)