Abstract: A method is disclosed for producing a flexible microcircuit of a size usable in vivo in the arterial or venous tract of a human. The method comprises forming, by various photoresist techniques, conductive runs on a polyimide base of about 1-2 mils thickness. Each end of a flexible microcircuit has minute holes formed therein for connection to an electronic chip and to hard wiring. The method produces holes in the conductive runs for the electronic chip connection of about 0.002 inches in diameter and holes about 0.016 inches in diameter at the end for wiring.