Carcinogenesis is widely believed to occur when regulatory systems governing cellular proliferation and differentiation are compromised. To date, various methods have been devised to determine cell cycle. However, these methods have not gained popularity in the diagnostic field. We developed a multiplex immunohistochemical method that can simultaneously stain cells in the G1 and S/G2/M phases and those undergoing apoptosis with the 3 markers Cdt1, geminin, and gamma H2A.X. The staining procedure can be performed using an autoimmunostainer. The nuclei of cells in the G1 phase stain red with the antibody for Cdt1, those in the S/G2/M phases stain blue with the antibody for geminin, and the nuclei of cells undergoing apoptosis stain brown with the antibody for H2A.X. The present method enables accurate cell cycle assessments using paraffin-embedded tissue specimens, which are superior to other forms of specimens in terms of morphologic observation.