AbstractRegeneration of olfactory epithelium was studied at the ultrastructural level in two different strains of mice (C57B1/6J and SWR/J) following destructive changes induced by nasal irrigation with a 1% aqueous solution of zinc sulfate (ZnSO4).Three epithelial conditions were seen during the first four to 14 days following treatment: a “surface alteration” state characterized by changes at the apical ends of olfactory and columnar supporting cells, a “squamous‐metaplastic” state, and a “simple‐squamous” state. In the latter two conditions, thought to represent regenerative states, cells contained inclusions similar to secretion granules in Bowman's glands. This observation supports earlier suggestions that new epithelial cells originate from these glands. Later regenerative changes consist of differentiation of new sensory cells and columnar supporting cells in an initially disorganized epithelium. This epithelium then changes to a normal, pseudostratified organization.Regeneration of the epithelium begins earlier and proceeds more rapidly in the SWR/J strain than in C57B1/6J mice. Possibly, a genetle difference exists between strains. After 72 days the epithelium in both strains