Cranberry juice contains high molecular weight non-dialyzable material (NDM) which was found to inhibit hemagglutination induced by the influenza virus (IV) as well as to neutralize the cytotoxicity of IV in cell cultures. Because influenza virus surface glycoproteins hemagglutinin (HA) and neuraminidase (NA) are involved in viral replication and in the infectious process, we sought in the present study to examine the effect of NDM on neuraminidases which are the target of most anti-influenza drugs today. NDM inhibited the NA enzymatic activity of influenza A and B strains as well as that of Streptococcus pneumoniae. This finding is of importance considering the emergence of influenza isolates resistant to antiviral drugs, reaching 90 % in some places. The anti-NA activity of NDM, evaluated by the MUNANA method and expressed as the concentration required for 50 % inhibition (IC50), was most potent against N1 (IC50, 192 microg/mL), less active against BN and N2 (IC50, 509 microg/mL and 1128 microg/mL, respectively), and moderately active against Streptococcus pneumoniae NA (IC50, 594 microg/mL). The in vitro findings of the present study suggest that cranberry constituents may have a therapeutic potential against both A and B influenza virus infections and might also interfere with the development of secondary bacterial complications