New pathways leading to a better understanding of the cell nucleus mor
pho-functional aspects are being opened up by cryofixation and cryosub
stitution methods. These techniques are able to produce excellent morp
hology of the nuclear fine structure with subtle, sometimes even notab
le, ultrastructural differences when compared with conventional chemic
ally fixed, dehydrated and embedded material. It is of particular inte
rest, when carrying out these cryotechniques, to avoid the use of any
cryoprotectant and chemical fixation. This permits an analysis of the
cell's fine structure, which may well approach its native state. Cryof
ixation, because of its extreme rapidity, should be able to immobilize
all cell activities and capture a well defined physiological state of
the cell without causing major changes in molecular structures. Immun
ocytochemical studies carried out using cryofixation and cryosubstitut
ion, gave very satisfactory results, often revealing antigenic sites w
hich were not, or hardly ever, detected when using conventional fixati
on techniques. The applications of various cryofixation and cryosubsti
tution methods in the study of the cell nucleus are summarized and an
attempt to critically evaluate their results is made in this review.