Observations have been made of J=2-1 CO in eleven circumstellar clouds including seven carbon stars and four oxygen-rich stars. Observations in four sources, including IRC+10216 have already been published (Wannier et al. 1979, henceforth Paper I) and the remaining observations are being prepared for publication (Knapp et al. 1980, henceforth Paper II). Several results are discussed below with special emphasis on the implications for two sources, namely IRC+10216 and Mira (o Ceti). The observations of IRC+10216 show CO emission over a diameter of 6 arcmin (∼ 0.5pc), a result suggesting a very large mass-loss rate. Mira is unique among the objects studied in displaying a small CO opacity and a high CO excitation temperature. It is suggested that this heating results from the orbital velocity of Mira due to its close binary companion.