Konowalchuk and Speirs had reported that viruses were inactivated in vitro by a variety of fruits and fruit juices (Konowalchuk and Speirs 1976a, b; Konowalchuk and Speirs 1978a, b) . Inactivation by apple juice was said to be irreversible (Konowalchuk and Speirs 1978a) . We focused on the effects of Concord grape juice, which inactivated CB3, EC6, and PO1 but not parainfluenza virus type 3 . Filtration of 32 P-labeled, inactivated PO1 through a 50-nm porosity polycarbonate membrane ruled out aggregation as a cause of titer loss. The inactivated virus showed limited attachment to homologous host cells but did not infect them. Treatment with polyethylene glycol (m.w. 20,000) reactivated the inactivated virus, as did human blood serum, indicating that the capsid had not been permanently modified. We had fed infant pigs human foods in an effort to make their GI tracts as nearly analogous to humans' as possible. We collected contents of stomach, duodenum, jejunum, ileum, cecum, and descending colon, and reacted these with grape-juice inactivated PO1 for 30 min at room temperature; the treated virus was reactivated 42-82%, depending on which GI contents were used. In addition to native virus, we used coproantibody-neutralized PO1 as a control; reactivation occurred with stomach, duodenum, and cecum contents, but not the material from other segments of the GI tract. It is unfortunate that the apparent reactivation of coproantibody-neutralized virus, which would have occurred upon ingestion, was not given more weight (not mentioned in the title, and only briefly in the abstract), as this finding may well have had greater public-health significance than the grape-juice results.