PBL's bioassays for interferons are cytopathic effect inhibition assays, also known as CPE and antiviral assays. Sample types include; tissue culture supernatents; serum from PK studies and delivery formulations. In these assays, one unit is defined as the quantity of interferon required per milliliter to reduce the cytopathic effect of viral infection by 50%. All standards used in our bioassays have been calibrated to the International Reference Standards such as those outlined by the National Institutes of Health [Pestka, S. (1986) Methods of Enzymology, 119, 14-23] and the World Health Organization. Results are normally provided 2-3 weeks after receipt of samples, although assay times may vary.