Persistent micro-albuminuria (MA) in patients with diabetes mellitus identifies a high-risk group for the development of vascular complications. Since the methodology involved in measuring MA has not been standardised, MA in 40 diabetic patients was measured in order to compare nephelometry with radio-immunoassay (RIA). The effect of storage (7 days), the influence of freezing and thawing on MA levels, and possible differences between glass and plastic containers were also assessed. An excellent correlation (r = 0.971) was found between RIA and nephelometry. Urine could be safely stored at 4 degrees C in either plastic or glass containers without any significant influence on MA concentrations. It is concluded that nephelometry is an excellent method for accurately measuring MA.