The detection of cells undergoing apoptosis in the Lin⁻ population. Mice were inoculated with 1 × 10⁵ PFU of MCMV. On day 3 pi, the mice were killed in order to remove their bone marrow cells. Using flow cytometry, the signals of PI, which represent the DNA contents, were examined after the Lin⁻ populations were gated. The G0/G1-peak was adjusted at channel 100 and subdiploid cells were designated as cells undergoing apoptosis. Before the experiments, it was confirmed that a coefficient variance in the PI-stained thymocytes was ca. 2%. The numbers in the figure represent the percentage of cells undergoing apoptosis in the Lin⁻ cells. *Significant increase versus uninfected control (P < .01).