  We have determined Li, C, N, O, Na, and Fe abundances, and 12C/13C isotopic
ratios for a sample of 62 field metal-poor stars (plus 43 taken from the
literature). This large sample was used to show that small mass lower-RGB stars
(i.e., fainter than the RGB bump) have abundances of light elements in
agreement with theoretical predictions from classical evolutionary models. A
second, distinct mixing episode occurs just after the RGB bump, reaching
regions of incomplete CNO burning. No O-Na anticorrelation, as observed in
globular cluster stars, is found in field stars. This means that the mixing
episode is not deep enough to reach regions where ON-burning occurs.
