Simultaneous immunocytochemical demonstration of the centrosphere and nucleolar organizer in cultured human cells

: A rabbit showing natural centrosphere-immunoreactivity was immunized with streptococcus pyogenes type 24 (S 24). During the immunization, an additional NOR-immunoreactivity appeared. This reactivity was not inhibited after the serum absorption by S 24 and seems fortuitous. The simultaneous immunoperoxidase technique staining centrosphere and NOR is described and illustrated during successive phases of mitosis. Unique as of this date, this serum may serve as a useful tool to study the centrosphere and NOR.