ABSTRACT
Nucleolar silver stained granules (SSGs) representing nucleolus organizer regions (NORs) were investigated in human as well as rabbit bone marrows after visualization with standardized silver reaction for non-histone nucleolar argyrophilic proteins. The results indicated that few mononuclear lymphoid blast-like cells in investigated bone marrows are characterized by large irregularly shaped nucleoli which contain a larger number of SSGs than myeloblasts or proerythroblasts as well as immature or stimulated lymphocytes. Since according to previous studies the number of nucleolar SSGs decreased in the course of the erythroid, granulocytic and lymphocytic differentiation and maturation, a possibility exists that the described mononuclear lymphoid blast-like cells are even less differentiated and immature than committed stem cells for mentioned cell lines.