To clarify further the relationships between parathyroid glands and the development of hypertension, we studied the effect of cross-transplantation of these glands from young hypertensive rats in normotensive recipients. The parathyroid glands were isolated in 5-week-old hypertensive rats of the Lyon (male and female) and Milan (only male) strains and immediately grafted into the corresponding, just parathyroidectomized normotensive rats of the same age. Control rats were either sham-operated or grafted with the glands of the same normotensive strain. Plasma calcium concentration immediately decreased after parathyroidectomy (PTX) and returned to near normal values 3 weeks after the graft. Systolic blood pressure increased slightly, but significantly, in normotensive animals grafted with hypertensive glands compared with that in normotensive control rats (mean increase, +9 mm Hg in males; +5 mm Hg in females). In conclusion, parathyroid gland transplantation from the hypertensive strain is able to chronically enhance blood pressure in the normotensive animal. The parathyroid hypertensive factor recently described may be implicated in these two hypertensive strains. Our data extend observations obtained previously in SHRs and stroke-prone SHRs and add further evidence for a major function of parathyroid glands in experimental hypertension.