Objective: To determine whether preexisting intrauterine vital infection is associated with postamniocentesis pregnancy loss. Methods: We accessed our bank of second-trimester amniotic fluid (AF) samples obtained aseptically and stored at -20C from all 11,971 women who underwent genetic amniocentesis between 1988 and 1995. Samples were retrieved from every case of spontaneous pregnancy loss within 30 days of the amniocentesis (excluding aneuploidy and anomalies, n = 66). Sixty-six control samples were randomly chosen from subjects who delivered at term and were matched for year of test, gestational age, maternal age, and indication for amniocentesis. Investigators were blinded to the status of the samples, which were studied by polymerase chain reaction (PCR) for the presence of adenovirus, parvovirus, cytomegalovirus, Epstein-Barr virus, herpes simplex virus, enterovirus, influenza A virus, and β-actin DNA. Results were compared with interleukin-6 (IL-6) levels previously measured by enzyme-linked immunosorbent assay in the same samples. Results: Sixty-two study cases and 60 controls were sufficient for all PCR studies. Fourteen AF samples contained a single virus: five (8%) of 62 study cases and nine (15%) of 60 controls (P = .27). Adenovirus accounted for nine (64%) of 14 viruses identified: four of 62 cases and five of 60 controls (P = .74). Cytomegalovirus was not identified in any study cases but was found in three controls. The mean IL-6 levels in samples with and without virus were not significantly different (4.8 ± 15.9 ng/mL with virus compared with 2.0 ± 8.8 ng/mL without virus; P = .53). Conclusion: Presence of virus in second-trimester AF is not significantly associated with elevated IL-6 levels or with early postamniocentesis pregnancy loss.