Polysaccharopeptide (PSP) isolated from the edible mushroom Coriolus versicolor was tested for its potential as an anti-human immunodeficiency virus type 1 (HIV-1) compound in a series of in vitro assays. It demonstrated inhibition of the interaction between HIV-1 gp 120 and immobilized CD4 receptor (IC50 = 150 microg/ml), potent inhibition of recombinant HIV-1 reverse transcriptase (IC50 = 6.25 microg/ml), and inhibited a glycohydrolase enzyme associated with viral glycosylation. These properties, coupled with its high solubility in water, heat-stability and low cytotoxicity, make it a useful compound for further studies on its possible use as an anti-viral agent in vivo.