Recently, certain batches of heparin have been associated with an acute, rapid onset of serious side-effects indicative of allergic-type reactions. These reports generated significant concern regarding the possible presence of a dangerous contaminant within heparin and highlighted the need to re-assess the purity criteria of heparin preparations for clinical use. Given the nature of the array of all possible contaminants, traditional screening tests cannot safely differentiate between contaminated and uncontaminated heparin preparations. Mono- and bi-dimensional NMR spectroscopy are powerful techniques that are able to detect and quantify a wide variety of potential sulfated polysaccharide contaminants. As such, these techniques are powerful tools for the analysis and assessment of heparin preparations.