Federal Republic of Germany

Ehrlich ascites tumour cells were extracted in buffers containing Triton X-100 and mono-, di- and polyvalent cations and then analysed by phase-contrast and electron microscopy. The results of this ultrastructural analysis confirm those of the biochemical analysis in the accom-panying paper that the stability of intermediate-sized filaments is dependent on the ionic environment. Furthermore, the organization of filaments in long parallel arrays is dependent on the presence of divalent cations and can be inhibited, to some extent, by the presence of monovalent cations. The stability of other detergent-resistant structures, the boundary lamina, microfilaments, microtubules, centrioles, polyribosomes and the nuclear cortex, is also affected by the ionic environment but to a lesser extent