Arrested divisions represent a defective type of germ cell division. The cells are irreversibly arrested in a state marked by strongly condensed chromosomes, a dissolved nuclear envelope and a disturbed spindle apparatus. They finally die. The present ultrastructural study of the ageing human seminiferous epithelium is the first to describe such cells in the human testis. The cells usually lie in small groups and show intercellular bridges connecting them. The bridges lack a bridge-partitioning complex, a structure otherwise characteristic for bridges between dividing germ cells of a clone. Frequently, arrested divisions show signs of cytoplasmic disorganization and severe structural degradation. Centrioles, irregular microtubules, small membranous vesicles and granular electron-dense material are crowded within the circle of chromosomes. Some cells show numerous small vesicles and larger membranous structures distributed throughout the cytoplasm. The presence of arrested germ cell divisions in ageing men might be connected with local dysfunctions of the Sertoli cell barrier, which are known to appear focally in the ageing human seminiferous epithelium as well.