The plant alkaloids castanospermine, dihydroxymethyldihydroxypyrrolidine and deoxynojirimycin have recently been shown to have potential anti-HIV activity [(1987) Proc. Natl. Acad. Sci. USA 84, 8120-8124; (1987) Nature 330, 74-77; (1987) Lancet i, 1025-1026]. They are thought to act by inhibiting alpha-glucosidase I, an enzyme involved in the processing of N-linked oligosaccharides on glycoproteins. We report here the relative efficacy of a spectrum of amino-sugar derivatives as inhibition of HIV cytopathicity. Several alpha-glucosidase inhibitors and alpha-fucosidase inhibitors were found to be active at concentrations which were non-cytotoxic.