Autopsy specimens from patients with Marburg disease having at least 10(4.5) TCID(50) of virus per gram of tissue were found to contain sufficient fluorescent antigen-positive cells to make a specific diagnosis possible in less than 3 h. Liver, heart, spleen, and kidney tissues were found to contain significant amounts of virus. Tissue suspensions, as well as blood or serum samples, inoculated into Vero cell cultures produced virus-specific immunofluorescence within 2-5 days. At least one specimen of all virus-positive persons yielded Marburg virus-specific antigen on day 2 or 3 after inoculation. Furthermore, tissues with at least 10(5.5) TCID(50) of virus/g had Marburg antigen of sufficient titre to be used in complement fixation tests.