We recently reported the frequent detection of polyomaviruses (BK virus [BKV] or simian virus 40 [SV40])in 46% of stool samples from hospitalized children. In order to determine if adults exhibit fecal shedding of polyomavirus, single stool specimens from healthy adults were evaluated by PCR. Overall, 20 (18.2%) of 110 specimens were positive for human polyomaviruses: 9 with BKV, 9 with JC virus (JCV), 1 with SV40, and 1 with both JCV and SV40. Among the 94 subjects without immune compromise, 17 (18.1%) were excreting polyomaviruses. This shedding frequency in adults was significantly lower than that observed in children (P < 0.001). These findings support the hypothesis that the gastrointestinal tract may be a site of polyomavirus persistence, and they suggest a fecal-oral route of viral transmission.Seroprevalence studies from various parts of the world have documented the ubiquity of early childhood infection with BK virus (BKV), a polyomavirus whose host-range is limited to humans (15,35). Infection with BKV has not been associated with any known clinical syndrome in healthy individuals, and BKV persistence is believed to be lifelong, primarily in the kidney and in leukocytes (32). BKV is occasionally excreted in the urine of healthy adults and children (20). BKV viruria may be common among pregnant women, perhaps reflecting the mild immune compromise of pregnancy (2, 10). Among kidney transplant recipients, BKV reactivation can lead to high titers of virus in the urine and the development of polyomavirusassociated nephropathy, which has emerged as a significant cause of renal allograft loss (13,17,18). After hematopoietic stem cell transplantation, BKV reactivation can cause hemorrhagic cystitis, a painful syndrome that usually resolves following engraftment of T-cell lineages (24,25).JC virus (JCV) infection occurs somewhat later in life, more commonly in the second and third decades (22). As with BKV, there is no recognized clinical syndrome associated with primary JCV infection, and it has emerged as an important cause of disease among severely immunocompromised patients (4,31,41). JCV reactivation in patients with AIDS and other T-lymphocyte deficiencies can result in progressive multifocal leukoencephalopathy, which is uniformly fatal in the absence of restored T-lymphocyte function. JCV has been detected in both colon and gastric cancers and adjacent normal tissues, suggesting that the gastrointestinal tract is a site of JCV persistence, but it has not previously been detected in feces (23,30,34,39). SV40 has been detected in urine and feces from humans and in mixed fecal and urine specimens from cynomolgus monkeys (3,39,40).Despite the ubiquity of BKV infection, its route of transmission has not been clearly determined. In addition to urinary excretion, BKV has been detected rarely in respiratory secretions and tonsil tissue (16, 37). It has also been detected in placental tissue, but whether it is transmitted in utero has not been determined (5, 28). Recent studies by our laboratory have detected po...