Interferon induction by administration of pyran copolymer was utilized in three patients in an attempt to treat chronic measles encephalitis (Dawson's encephalitis). Although the course of the disease was not effected by interferon induction, administration of the drug produced hematologic and urinary alterations resembling the hemolytic-uremic syndrome in one patient. Hematologic studies in two additional patients documented the heparin-like nature of pyran copolymer, and the production of a late hypercoagulable state following its administration.