Abstract: The present invention relates to antiteicoplanin polyclonal antibodies raised against a composition consisting of teicoplanin encapsulated in negatively-charged liposomes and the antibodies are not immunoreactive with any other antibiotics. The present invention relates to a method for determining the amount of teicoplanin in a biological sample, which comprises the steps of a) incubating anti-teicoplanin antiserum of the present invention with a biological sample containing an unknown amount of teicoplanin on a solid support; b) incubating anti-teicoplanin polyclonal antibodies of the present invention in serum with a standard containing a known amount of teicoplanin on a solid support; and c) determining the presence or absence of agglutination in step a) and b) whereby determining the unknown amount of teicoplanin present in the biological sample by comparing with the complete inhibition of agglutination of step b).