The pharmacokinetics and pharmacodynamics of recombinant human interferon beta (IFN-beta-1a) were compared after intramuscular administration of two preparations (Rebif(R) and AvonexTM) and subcutaneous administration of Rebif(R). Healthy volunteers (n = 30) received a single dose (60 µg) of each of the three treatments in a randomised crossover study. Serum concentrations of IFN-beta were measured by enzyme-linked immunosorbent assay over 24 h after dosing. Pharmacodynamics were assessed by measurement of intracellular 2',5'-oligoadenylate synthetase activity, and serum neopterin and beta2-microglobulin concentrations, over 144 h after dosing. There was no significant difference between the three treatments in peak serum IFN-beta concentrations (Cmax) or area under the concentration-time curve (AUC). No significant differences in pharmacodynamic measures were observed between the three treatments. It is concluded that the bioavailability of IFN-beta-1a is equivalent after subcutaneous or intramuscular administration of Rebif(R), and intramuscular administration of AvonexTM. Copyright Rapid Science Ltd