Spectra of binaries classified as lambda Bootis stars

High angular resolution observations have shown that some stars classified as lambda Boo are binaries with low values of angular separation and magnit ude difference of the components; therefore the observed spectrum of these objects is a combination of those two components. These composite spectra h ave been used to define spectroscopic criteria able to detect other binarie s among stars classified as lambda Boo. The application of this method to H D 111786 is presented: the contribution of 5 components to the observed spe ctrum is demonstrated by the shape of the O I 7774 Angstrom feature. This r esult makes unreliable any attempt to perform an abundance analysis of this object which therefore must be definitely rejected from the class of the p eculiar lambda Boo stars. This approach allowed us also to recognize that t he SB2 star HD 153808 is in reality a triple system.