After a concise review of the history of why the embedment-free section transmission electron microscopy (TEM) was developed, two major characteristics/advantages of this method were described: 1) enhanced electron-translucency of bio-specimens, and 2) disclosure of strand networks occupying the cytoplasmic matrix. The former advantage, the main issue of this review, makes it possible to see-through superimposed laminated targets when viewed en-face. Ultrastructural features of the basement membranes in the renal glomerular filtration barrier of rats and in the synapse of Torpedo electrocytes, and those of thinner myelin sheaths were noted as 3D examples of this electron-translucency. Such seeing-through of the basement membranes disclosed regional structural heterogeneity suggesting their remodeling and dynamics. It also has the potential to analyze the spatial interrelation of bioactive molecules localized in the superimposed compartments partitioned by the laminated targets. As for the latter advantage, though avoiding its details in this review, the possibility has repeatedly been proposed that the cytoplasmic networks as a whole, but not individual strands themselves, represent the concentration of cytoplasmic matrix proteins and their sol or gel status. The possible interpretation of the cytoplasmic networks as representing the cytoplasmic sol-to-gel transition may shed new light on understanding the mechanisms of intracellular dynamics discrete from the known idea on the cytoskeleton. With its two characteristics/advantages in consideration, the embedment- free section TEM is still worth attracting more attention in ultrastructural analyses of bio-specimens.

KEY WORDS: Embedment-free section; Electron-translucency; en-face basement membranes; Cytoplasmic strand networks; Cytoplasmic sol-to-gel.