Importance of non-LTE effects. Left panel: comparison of synthetic line profiles for the Mg II λ9632 Å blend to DIB λ9632Å in HD 165784, for the average magnesium abundance derived for the star: non-LTE (solid line), LTE (dashed line), LTE profile for an adjusted abundance that allows the non-LTE EW to be reproduced (dotted line: identical to the solid line in this case). The profiles were convolved with the appropriate broadening functions for the star. Right panel: same as in the left panel, but for He I λ11970 Å blend to DIB λ 11970 Å, for HD 183143 (see text for discussion).