The serum of 88 chronic fatigue patients was screened for enteroviral specific sequences by polymerase chain reaction (PCR) assay. The PCR method used was "nested" PCR targetting the 5' nontranslated region of the enteroviral genome which yielded a final fragment length of 264 base pairs. Samples were obtained from patients during 1990-1991. In addition, buffy coat specimens and stool specimens were examined in some patients. Samples from two cohorts of comparison individuals were also obtained. The comparison groups were firstly, acutely ill individuals with symptoms consistent with a presumed enteroviral infection (matched by age, sex, and date of receipt of specimen) and secondly, healthy individuals (matched by age and date of receipt of specimen). Enteroviral specific sequences were detected in 36 of 88 serum samples from chronic fatigue patients, 22 of 82 acutely ill individuals, and 3 of 126 healthy individuals. The enteroviral PCR positivity did not correlate with any one particular feature of chronic fatigue nor did it reflect any history of illness at onset of fatigue, duration of fatigue, or age of patient. These results provide new evidence for the presence of enteroviral specific sequences in serum, buffy coat, and stool samples in many patients with chronic fatigue. This may reflect a persistent enterovirus infection in a proportion of chronic fatigue patients.