One hundred forty-seven stool specimens from 93 infants younger than four months of age in a Neonatal Intensive Care Unit were tested for rotavirus by the Rotazyme ELISA method (Abbott Laboratories, North Chicago, IL). None of the infants had diarrhea at the time of the testing. Ten of 147 (6.8%) specimens were either low or suspect positive. None had rotavirus by electron microscopy. Excluding the suspect positives, which were negative on retesting, the false positive rate was only 6 of 147 (4.1%). Of five specimens with sufficient material and repeatedly positive tests, heat to 56 degrees C for one-half hour eliminated the binding to the Rotazyme bead but had no effect on the rotavirus positive control. One patient was found to have an extremely high positive Rotazyme test, independently of the survey. No virus was found in this specimen by electron microscopy, and the material responsible for the false positive result was not removed by centrifugation (100,000 X g for one hour), heating to 56 degrees C for one-half hour, trypsin, ether/beta-mercaptoethanol, or dialysis. Thus, false positives were encountered, but the overall rate was acceptably low. Such false positives are likely to result from more than one cause and, depending on results of further study, may be confirmed as false positives by loss of reactivity at 56 degrees C for one-half hour and perhaps lack of binding to a control bead.