Excited20Ne at 0.1 torr was placed inside the cavity of a single‐frequency, 6328‐Å laser. A pronounced peak appeared in the output power, caused by an inverted Lamb dip effect. Because of the low pressure used, this peak was only 30 ± 5 MHz wide and must be very near the atomic resonant frequency. In contrast, the overall output curve was blue‐shifted 60 ± 10 MHz by the 3 torr nominal pressure in the laser gain tube. This saturated absorption effect can be used as an absolute reference for the frequency stabilization of He&sngbnd;Ne and similar lasers.