SummaryThe electron microscopic changes in rabbit inferior vena cava in partial obstruction resemble the ultra‐structural vascular response to other types of alteration in cellular environment. First there is an appearance of hyperactivity and metabolic stimulation with deposition of elastin and collagen fibres and reversion of cells of intima and media to a more primitive type. Later, following subsidence of activity, there is apparent cellular degeneration and tissue simplification.