Enteroviruses attracted attention to coproantibody (presumably IgA) because they are shed for prolonged periods (often weeks) and are neutralized by coproantibody during the later part of the shedding period. Our first interest had been in how coproantibody might interfere with virus detection in cell cultures; the study just described was perhaps the first to show that coproantibody-neutralized virus is quite likely infectious if ingested. After extraction from potato salad by our early Freon method, PO2 was completely reactivated if it had been neutralized with coproantibody, but it was only partly reactivated if neutralized with hyperimmune rabbit serum (presumably IgG) (Herrmann and Cliver 1968b) . Some laboratories have been reluctant to use Freon, for various reasons. We later showed that coproantibody-neutralized PO1 extracted from ground beef could be reactivated by treatment with pancreatin (an extract of bovine pancreas containing a variety of proteases and other enzymes); the resulting extract could be tested as much as 35 ml per 25-cm 2 cell culture, and could be passed among different types of cell cultures, to detect cytopathic viruses (Kostenbader and Cliver 1986) .