The effect of temperature on the stability of the Varian V‐4300–2 NMR spectrometer has been investigated. The spectrometer was most sensitive to changes in room‐air temperature. A change of 0.3°C per minute caused a spectrometer drift of about 20 cps per minute. A change of 0.1°C per minute in temperature of magnet cooling water caused a spectrometer drift of 1 cps per minute. Enclosing the magnet served to minimize effects of air temperature changes but amplified the effects of water temperature changes. Satisfactory control was attained by running the refrigeration units continuously and regulating the temperatures by controlling the suction pressure on the evaporators. Under these conditions spectra were reproducible to within ½ cps.