Ergosterol peroxide (5ñ,8ñ-epidioxy-22E-ergosta-6,22-dien-3ò-ol) is a steroid derivative. It has been isolated from a variety of fungi, yeast, lichens and sponges, and has been reported to exhibit immunosuppressive, anti-inflammatory, antiviral, trypanocidal and antitumor activities in vitro.