The aim of this study was to evaluate the (1) functional density (FD), (2) afferent (AFD), apical (APD) and efferent (EFD) diameters, (3) red blood cell velocity (RBV), maximum red blood cell velocity (RBVmax) after 1 min ischemia and the time to reach it (TRBVmax) in nailfold capillaries in controls and systemic lupus erythematosus (classified according to the American College of Rheumatology) patients. This is a controlled clinical trial, matched by age and sex with 22 out patients and 14 healthy volunteers. The study was approved by the Ethical Committee of the University. Diabetes mellitus, primary arterial hypertension, other connective tissue diseases, cancer, AIDS and hepatitis C were excluded. The mean values obtained for patients versus controls, respectively, were (mean +/- SD): FD (per mm(2)) 7,5 +/- 1.9 and 8 +/- 1.62; AFD (mum) 9.5 +/- 2.0 and 11.0 +/- 1,5; APD (mum) 13.6 +/- 0.6 and 16,4 +/- 2.4; EFD (mum) 10.6 +/- 2.5 and 13 +/- 1.7 (p=0.01); RBV (mnVs) 0.97 +/- 0.3 and 0.9 +/- 0.4; RBVmax (mm/s) 1.5 +/- 0.5 and 1.73 +/- 0.9 and TRBVmax (s) 5 +/- 1.4 and 4.5 +/- 0.85. Our results do not show significant differences between the groups examined, except for the diameter of the efferent capillary loop.