Scedosporium prolificans is a filamentous fungus that causes localized infection restricted to bone and soft tissues in immunocompetent patients and disseminated infections in immunocompromized patients with organ transplants or neutropenia. Now compared is the antigenic composition of its mycelial peptidorhamnomannan (PRM-Pb) with that of related Pseudallescheria boydii, the teleomorph stage of S. apiospermum. P. boydii , the etiological agent of pseudallescheriasis, contains an PRM, which is a potential diagnostic antigen, with Rhap-(1®3)-Rha epitopes linked (1® 3)- to Manp [1]. Reductive, alkaline b -elimination of PRM provided more structural details as nonreducing oligosaccharides, which were separated by gel filtration into oligos-1, -2 and –3. The major oligo-1 was branched with a main chain of a -Rhap-(1® 3)-a -Rhap-(1® 3)-a -Manp-(1® 2)-Man-ol, substituted at O-6 with an a -Glcp-(1® 4)-b -Galp group. [2]. S. prolificans was extracted with hot phosphate buffer, pH 7.2, followed by precipitation with Cetavlon in the presence of sodium tetraborate. The precipitate (PRM-Sp) contained carbohydrate (63%) and protein (35%) with Rha, Ara, Man, Gal, and Glc in a 31:2:44:13:10 ratio. Methylation data showed Glcp-(1®4)-Galp- groups to be absent. The structural differences of S. prolificans and P. boydii PRMs consisted of the former having a higher proportion of (1® 2)- over (1® 3)-linked a -Rhap units in the external region. These structural differences were consistent with ELISA antigenicity tests, carried out with hyperimmune rabbit antiserum against mycelial forms of P. boydii. The PRM-Pb of P. boydii reacted strongly, but less so with S. prolificans PRM-Sc. The role of this surface glycoconjugate in cell adhesion and the endocytosis process was also demonstrated.