Using a new ultra miniature pressure sensor hydrostatic pressure in renal tubules and renal blood capillaries was continuously recorded. The transducer was mounted in a special plexiglas device which was fixed on a micromanipulator. With a glass capillary attached to one end of the plexiglas block tubules and capillaries were punctured using conventional micropuncture techniques. The volume displacement of this transducer is about 1 nl/10 mm Hg. The recorded signal was found to be linear up to 300 mm Hg. The frequency of the system was highly dependent upon the capillary tip diameter. Examples of recorded pressures in renal tubules and blood capillaries are given.