Severe combined immunodeficient (scid) and BALB/c mice were experimentally infected with murine cytomegalovirus (MCMV). Scid mice infected by the intraperitoneal route died or were moribund at dose-dependent times ranging from 12 to 13 days after inoculation for > or = 3.00 x 10(4) plaque forming units (pfu) of virus to 25 days for 1.17 x 10(2) pfu. Histologic lesions included severe adrenal necrosis at low doses and splenic necrosis at high doses. Multinucleate hepatocytes with multiple inclusion bodies were observed at all doses. In visceral organs, the inflammatory response consisted of cell necrosis and neutrophil infiltration. Scid mice infected with 1.00 x 10(3) pfu by the intranasal route were moribund by 24 or 25 days after inoculation. Viral titers in tissues examined from these mice increased in all organs examined until they became moribund. BALB/c mice infected intranasally had detectable virus titers in the adrenal glands, salivary glands, lungs, and spleen by 7 or 14 days after inoculation, but decreased thereafter. These mice remained clinically normal through the infection. In BALB/c mice, histologic lesions were present only in the salivary glands.