The EM features of cytomegalovirus hepatitis in the liver biopsy of a 3 wk old infant were studied. The liver cells did not contain virus, but severe alterations similar to virus hepatitis were observed. In the bile duct cells, nuclear and cytoplasmic virus inclusions were demonstrated. In the nuclear inclusions virus particles of various degrees of maturity were embedded in dense granular material. The cytoplasm of the infected cells contained vacuoles with mature viruses. The Golgi zone seemed to play an important role in vacuole formation. In another type of infected cell, viruses were lying free in the cytoplasm and passed into the lumen of the bile ducts. It is concluded that viruses are eliminated by the bile. Based on this EM observations, the examination of duodenal fluids is recommended as a new diagnostic procedure for demonstrating viruses.