Abstract Single submandibular glands, single parotid glands or the combined three major salivary glands, were intraperitoneally isografted from female BALB/c donor mice. Without further treatment, surviving graft tissues consisted predominantly of hyperplastic duct-like structures throughout the 12-month investigations. Hyperplastic proliferation declined in intensity after showing strong features one week after grafting but instead of disappearing, it became again more active 12 months after transplantation. In any of the above-mentioned grafts, isoproterenol administration, prior to and following isografting, demonstrated that remarkable hyperplastic changes, some hardly microscopically distinguishable from an adenocarcinoma, could be induced. Post-transplantational treatments with either testosterone enanthate (20 mg fortnightly) or estradiol valerate (1 mg or less fortnightly) could accelerate hyperplastic alterations of duct-like structures surviving in the grafts and cause changes at 6 months after grafting which resembled those observed in untreated controls at the 12-month interval. In surviving duct-like structures, acini and secretory tubules reappeared following administration of isoproterenol and testosterone, respectively. However, these reappearing cells have never undergone hyperplasia. These phenomena suggest that only de-differentiated duct-like structures are capable of undergoing mitoses and becoming hyperplastic but, after re-differentiation, cells lose their capability.