Our investigation included 20 patients with rheumatoid arthritis and a negative routine (albustix) proteinuria test, and 20 healthy controls. The albustix test was compared with a method based on multifractional Cellogel RS electrophoresis of urinary proteins. The albustix test was found to be not reliable in patients with RA. Microproteinuria was in fact detected by the electrophoresis method in 12 out of 20 RA patients. Eleven patients showed glomerular type proteinuria (which was "selective" in 5 patients and "non-selective" in 6 patients), and 1 patient showed mixed type proteinuria. Electrophoresis failed to show microproteinuria in the controls. The high sensitivity, easy handling and low cost of multifractioned electrophoresis (which does not involve disturbing the patients) suggest its introduction as a routine test for all RA patients, thus achieving both accurate clinical assessment of proteinuria and a rational therapeutic approach.