Electron-microscopic examination of rats renal glomeruli revealed that Zlábek’s thin intercapillary anastomoses (TIAs) are thin vessels which interconnect the ordinary glomerular capillaries, while branching off abundantly. The lumens of the TIAs are irregular, mostly closed, frequently cleft-like; the width of lumens is about 0.9–0.1 µm. The TIAs are situated in the intercapillary (mesangial) areas of renal glomeruli; they represent a special equipment which probably influences the glomerular plasma flow rate and the glomerular ultrafiltr