All types of interferon (alpha, beta, gamma) have a virostatic immunomodulating and antiproliferative effect. There are, however, quantitative differences between different interferons as regards the mentioned properties. Interferon beta has a marked antiviral action, and therefore it is used in a dose of 0.5 x 10(6) IU/kg in long-term infusions in life-endangering viral infections. Interferon beta differs from interferon alpha by a higher lipophilia and thus greater tissue affinity. It is therefore useful for local treatment. Local administration is used in severe infections of the anterior segment of the eye and in relapses of condyloma accuminatum and in warts. In oncology intra- and peritumourous administration is used which in the great majority of patients leads to a time-limited remission of metastases in soft tissues as well as in bones. Intrathecal interferon beta administration retarded in s minor group of patients the course of multiple sclerosis.