Process for drying medicinal plants

A process for drying medicinal plant materials so that a greater portion of the key active chemical components containing non volatile, large molecular weight active ingredients are retained in the dried plant materials comprising loading cut pieces of fresh plant materials into a vacuum microwave drying chamber, reducing the pressure in said chamber to a low pressure below 8 inches of Hg absolute pressure, applying microwave power at a first rate to said materials while at said low absolute pressure with a power density of between 1 and 12 kilowatts per kilogram of said fresh plant material for a time period of from 2 to 35 minutes while maintaining the temperature of the plant materials below 60.degree. C. to achieve an uniform drying of the plant materials to a moisture content of less than 20% based on the dry weight of the plant materials without permitting significant oxidation of said non volatile, large molecular weight active ingredients significantly damaging said plant materials by burning.