Abstract
A simple method of vital staining of nuclei or chromosomes in mouse eggs, sperms or embryos was developed. Use of a DNA-speciflc dye, Hoechst 33342 permits us to observe chromosomes easily in the mouse eggs in a living state under fluorescent microscopy. Stained sperm heads were also visualized in fertilized eggs. This dye exerted almost no inhibitory effects on both the processes of fertilization and subsequent (pre-and postimplantation) development.
