Chromosomal centromeric dots (Cd) of peripheral blood in 20 couples with spontaneous abortion and 10 normal couples were studied by Cd-banding technique. The frequencies of Cd loss and centromeric dots-nucleolar organizer region (Cd-NOR) fusion were 0.36 +/- 0.15/cell and 0.31 +/- 0.20/cell in the couples with abortion, 0.22 +/- 0.13/cell and 0.20 +/- 0.19/cell in normal couples respectively. These results showed that frequencies of Cd loss and Cd-NOR fusion in couples of spontaneous abortion were significantly higher than those in the normal couples. We suggested that the occurrence of spontaneous abortion in human might casually relate to the changes of Cd.