The invention concerns a method for producing, on an industrial scale, capsular polysaccharide of Haemophilus influenzae type b (PRP) intended for vaccine purposes, according to which a strain of Haemophilus influenzae type b (Hib) is cultured in a culture medium, the culture supernatant is harvested and treated in order to extract the capsular polysaccharide therefrom, said culture medium comprising at least: —one source of carbon, —protoporphyrin, —salts, —amino acids, —NAD or NADH, —vitamins, —means for regulating the pH, characterised in that said culture medium is chemically defined.
