In a nuclear magnetic resonance probe, the sample coil is connected to the RF excitation source via transmission lines that are arranged to generate one or more nodal points at the .sup.1H excitation frequency along their lengths and a balanced magnetic filed profile within the sample coil. Heat exchangers are then connected directly to the inner conductor of the transmission line at these nodal points. The transmission line inner conductors are in direct contact with the sample coil and efficiently cool the coil to cryogenic temperatures without interfering with the .sup.1H resonance or RF profile.