IN a recent publication we reported the detection of linearly polarized OH emission from a localized region near the radio source W3 (ref. 1). Although the mechanism of production of the polarized emission was not understood, we pointed out that, among several possible mechanisms, the Zeeman effect was unique because it alone would give rise to circularly polarized radiation. This communication reports observations made with a circularly polarized feed horn on the 140 ft. radio telescope of the National Radio Astronomy Observatory, Green Bank, West Virginia, between November 11 and 12, 1965. The-receiver used was an autocorrelation-type radiometer with 100 channels2. Bandwidths of 2.5 Mc/s, 625, 250, 62.5 and 15.6 kc/s could be studied with a frequency resolution of 0.012 of the bandwidth. Therefore, on some occasions, our maximum frequency resolution was 190 c/s. The system temperature, including losses in the antenna feed line, was 250° K; the antenna beamwidth was 19 min of are; coupling between the two senses of circular polarization in the antenna feed horn was approximately − 15 db.