We present the results of the analysis of an extensive set of new and literature high quality data concerning Fe, C, N, O, Na, and Mg. This analysis exploited the T_eff_ scale determined in Gratton et al. (1996, Cat. <J/A+A/314/191>), and the non-LTE abundance corrections computed in Gratton et al. (1999, Cat. <J/A+A/350/955>). Results obtained with various abundance indices are discussed and compared.