Clinical and laboratory features of 86 infants admitted with diarrhea and dehydration were evaluated prospectively. Human rotavirus (HRV) infection was documented in 35 infants (41%) by the Rotazyme test. Those with HRV gastroenteritis (HRV+ group) had a shorter duration of diarrhea prior to admission, more severe dehydration on presentation, and a longer hospital course than the HRV-negative (HRV-) group. Vomiting, fever, upper respiratory tract symptoms, otitis media, and cough were present in equal numbers of infants in both groups. The HRV+ infants had lower serum bicarbonate and higher serum albumin, alanine aminotransferase, aspartate aminotransferase, and uric acid concentrations than did the HRV- infants. Serum uric acid levels greater than 10 mg/dL (590 mumol/L) were present in 69% of HRV+ vs 29% of HRV- infants. The Rotazyme test was found to be a valuable tool in diagnosis; testing on two days increased the yield from 74% to 97% of all infants finally diagnosed as HRV+. The optimal time for testing was within the first five days of illness.