This paper focuses on the problem of decoupling transmitter and receiver coils when noise arises predominantly from the coil resistor, the general case in high-resolution NMR as well as in NMR of small biological samples. Test procedures for assessing the efficiency of decoupling schemes are proposed. It is shown that the residual current flowing in the decoupled coil, which distorts the magnetic field profile of the working coil, may be easily calculated from comparison of the resonance frequencies of the isolated coils and of the combined coils. It is also pointed out that the measurement of the modification of the quality factor of the receiver coil due to the introduction of the decoupling component inaccurately reflects the increased losses. These principles are demonstrated in the case of coaxial surface transmitter and receiver coils. The severe problems caused at high frequency by earth loops and capacitive coupling between components have been circumvented by designing all circuits and coils in an electrically balanced manner. Particular attention has been paid to the receiver coil, and a solution based on the use of twin lines is described which preserves the sensitivity of the coil even with lossless samples. (1995 Academic Press, Inc.