First we discuss a method of tuning NMR probe circuits and matching impedances which employs a variable length transmission line as one of the tuning elements. This method is useful for high voltage circuits where, due to space considerations, suitable tuning elements may not be placed adjacent to the rf field‐producing coil. Second, we describe the design of a single coil double resonance probe which uses &lgr;/4 transmission lines as filters as well as tuning elements. This double resonance probe is useful when the two frequencies of interest are widely separated.