A unique minimally invasive system for painless blood testing is now being commercialized for measurement of blood glucose concentration by diabetics. The novel component of this system, a consumable microsampling and assay device, consists of a tough, flexible silicon microneedle comparable in cross-section to a human hair integrated with a silicon microcuvette. This microneedle is capable of reliably taking a very small sample of whole blood completely painlessly, unlike sticks with the much larger metal lancet that must be used in all other current systems. The device permits a one-step process that avoids the need to transfer blood from a skin puncture to a test strip, thus minimizing blood required and possible mess. The small hand-held instrument containing the consumable is touched to the skin of the arm or any other part of the body, not necessarily the tip of the finger, and held there for one second. During this time, the microneedle is advanced and then withdrawn under microprocessor control, puncturing the skin and drawing less than 200 nanoliters of blood into the microcuvette, where the assay is performed automatically. The instrument calculates the blood glucose concentration, displays the result, and holds it in memory for recall. The consumable is produced by silicon microelectromechanical systems technology and can be produced in high volume at low unit cost. This technology shows promise of being extended to other analytes and to continuous monitoring.