A high-pressure microwave digestion system has been designed based on the concept of using large-bore tubes as digestion vessels and capsules as a vehicle for sample introduction. Many of the design aspects are dictated by the use of a relatively large (8.4 mm o.d., 25 mm long) capsule, which in turn dictates the inner tube dimensions. A variety of materials were studied for use as the tubing material. PFA was selected as the best material for a demonstration arrangement. The cycle of operation involves insertion of the capsule by a flexible rod followed by addition of digestion reagent and then a heating/cooling/venting cycle for removal of gases. When the digestion is completed, the system removes the liquid with the same flexible rod and then cleans itself. The system is highly automated with computer-controlled venting, cooling, and reagent addition. Data indicate that performance is similar to that expected of a conventional microwave oven operated at the same temperatures.