In 672 newly-diagnosed, Type 2 (non-insulin-dependent) diabetic patients without urinary infection, aged 51 (9) years, mean (1 SD), 28% of patients had raised albuminuria, defined as albumin excretion greater than 25 mg/l and 66% raised urinary N-acetylglucosaminidase excretion defined as greater than 300 mumol.h-1.l-1 (both urinary analytes corrected by linear regression on urinary creatinine to 10 mmol/1). In a univariate analysis, urinary N-acetylglucosaminidase and albumin excretion correlated with each other (rs = 0.42, p < 0.001), and with fasting plasma glucose (rs = 0.46 and rs = 0.27, p < 0.001, respectively). The association of urinary albumin and N-acetylglucosaminidase remained significant after taking the fasting plasma glucose levels into account, partial rs = 0.34, p < 0.001. After 3 months of dietary therapy BMI decreased from 29.7 (5.9) kg/m2 to 28.8 (5.8) kg/m2, fasting plasma glucose levels from 12.2 (3.8) mmol/l to 9.8 (3.8) mmol/l, and systolic blood pressure from 143 (21.8) mmHg to 131 (20.3) mmHg, p < 0.001 for each variable. There were concomitant decreases in urinary N-acetylglucosaminidase, geometric mean (1 SD interval), 397 mumol.h-1.l-1 (216 to 728) to 291 mumol.h-1.l-1 (160 to 528), p < 0.001 and in albumin excretion 16 mg/l (5 to 51) to 13 mg/l (4 to 40), p < 0.001. The decrease in urinary N-acetylglucosaminidase, but not the decrease in urinary albumin excretion, was associated with the initial degree of glycaemia and the decrease in glycaemia in response to diet.(ABSTRACT TRUNCATED AT 250 WORDS)