A number of natural and synthetic sugar analogues have been tested for their antiviral activity, using an influenza virus strain as a model. Hemagglutinating titres (HA) and cytopathic effect (CPE) were surveyed to estimate the virus production. It was found that introduction of the benzyl group into these sugars generally causes them to become antivirally active. Substitution with methyl, acetyl, uridyl and thiocyanyl groups or derivatization with azido, isopropylidene and benzylidene groups were without effect. All sugars containing the 2-deoxy-2-acetamido group were inactive.