Interferons can be chemically and enzymatically altered to obtain molecular forms which differ in size, charge, and/or host-range from native interferons. These data suggest that small active cores of interferons can be obtained which may possess more desirable characteristics than native interferons, such as lack of "species-specificity"" and increased stabilities. Studies for assessing alterations of interferons due to chemical or enzymatic treatments must monitor the treated interferons for changes in ratios of each of the various activities attributed to native interferons and must characterize the altered interferons in terms of each of the physical and biological markers.