Abstract: A simple cell-synchrohization technique by BrdU treatment in vitro was described in this paper.More prophase and prometaphase cells may be obtained by this technique.The chromosomes revealed distinct R- bands and G- bands on the same preparation after special staining.The different proportion of R- bands and G- bands in 4 species of Mammals (human,red muntjak,black muntjak,and Chinese hamster) have been reported.The technique described her may be of interest as an easy method for inducing banding patterns of chromosomes.