ECHO virus is an intestinal virus that can cause fever, inflammation of the brain and spinal cord membranes, and respiratory disease. Previous studies have indicated that ECHO virus can cross the placental membrane and infect the fetus. A few reports have appeared that describe birth defects and spontaneous abortion of the fetus caused by ECHO virus infection of the mother. There is little information available about the risk factors, sources of infection, and method of transmission of the ECHO virus. This article describes the cases of three pregnant women who had ECHO virus infections that resulted in two cases of spontaneous abortion and one stillbirth. Three out of 78 pregnant women examined were infected with ECHO virus. Two different strains of ECHO virus were isolated. ECHO virus type 33 was present in the fecal samples of the two mothers that experienced spontaneous abortion during the second trimester, and the same type of virus was found in the placenta and in the fetal kidneys, liver and brain. ECHO virus type 27 was found in the placenta, heart, kidneys, liver and brain of the fetus that was carried to term, but was dead at birth. The results of this report, along with those of other reports, suggest that ECHO virus infection may be a more common cause of neonatal and fetal mortality than was previously thought. There is a need to develop methods of preventing ECHO virus infection in pregnant women. (Consumer Summary produced by Reliance Medical Information, Inc.)