The sensitivity of continuous-wave NMR can be increased with a high- Q resonance tank circuit by using superconducting wire and a GaAs FET preamplifier operating at liquid helium temperatures. We discuss impedance matching to obtain an optimal signal-to-noise ratio for input circuits operating at ≈500 kHz, with Q≈10 3–10 4 at an impedance level of 1 Mω and a noise voltage of 1.3nV/√Hz. High rf compensation of 1:10 5 is achieved with orthogonally oriented transmitter coils and an astatically wound pick-up coil. The performance is evaluated on the basis of resolution that we achieved in the measurement of the NMR line in normal liquid 3He; this is better than 1 part in 10 3 of the peak amplitude, while in the integrated intensity the standard deviation from the mean is better than 0.3%.