Principles are discussed for determining moisture content of individual peanut, Arachis hypogaea L., kernels by microwave resonator measurements, and data illustrating the application of these principles are presented. By measuring the shift in the resonant frequency and the change in the cavity transmission characteristics when a peanut kernel is inserted into the cavity, and taking the ratio of these two parameters, it is possible to obtain the moisture content of the kernel independent of its mass (size) and apparently independent of peanut type, as far as runner and virginia market types are concerned. Moisture contents in the range from 4 to 14 percent, wet basis, were determined with an uncertainty of 0.9 percent moisture, at the 95-percent confidence level.