Anti-correlation of Na and O abundances in stars of NGC 6388 in different evolutionary phases. In all three panels on the left, open circles are our total sample. In the top left panel, we plot RGB stars as filled circles. In the middle and lower panels, we superimpose values for RHB and AGB stars, in red and blue filled circles, respectively. In the right column, we show the observed distributions of the [O/Na] abundance ratios for RGB, RHB, and AGB stars, from top to bottom, respectively.