The invention relates to a method for assaying the teichoic acids present, most commonly in residual form, in a preparation of Gram+ bacterial antigens. This method requires, first of all, a controlled hydrolysis with hydrofluoric acid at a temperature of less than or equal to 40.degree. C., in order to release the oligosaccharides specific for teichoic acids. The assaying of the specific oligosaccharides can then be carried out by various techniques, in particular by high performance chromatography coupled with pulsed amperometric detection (HPAEC-PAD). The method according to the invention can in particular be used to assay the residual amounts of teichoic acids present in preparations containing capsular polysaccharides of Streptococcus pneumoniae, which may be useful as vaccines.