Stepronin is clinically used as an expectorant. It inhibits airway secretion in vitro by both decreasing Cl- secretion from epithelial cells and mucus glycoprotein secretion from submucosal glands. The mucolytic activity of stepronine does not involve the gastric mucous coating and that the drug does not exert adverse effects on the gastric mucosa. It is a new chemical immunosuppressant drug, which has the effect of preventing graft-versus-host-disease (GVHD) in a mouse model. The mechanism by which this compound acts as an immunosuppressant appears to be similar to cyclosporine A (CyA), although, in contrast to CyA, it is not toxic for animals and humans. Stepronin has an antiviral effect as well and is able to block, indirectly, the human immunodeficiency virus–1 (HIV-1) replication in mononuclear cells in vitro.