  Stromgren indices v and b are combined with broad-band index I, and a new
index p, the short wavelength half of the v band, to estimate CN 4215A
molecular absorption in a sample of stars in M22. The results have been used to
estimate carbon and nitrogen abundances and suggest groups of stars within this
cluster, each with a characteristic nitrogen abundance, but with a range of
carbon abundances. The results suggest the possibility of stars consisting of
material which has undergone CNO recycling two or three times. The method can
be subsequently used for other globular clusters.
