This work is based upon a series of quantitative morphological studies of the parathyroid glands of Mongolian gerbils and rats. Standard stereological methods were used on light and electron microscopical levels. Subclassification of the chief cells based on the staining affinity and electron density of the cytoplasm was not correlated with contents (volume and surface densities) of organelles. Compared to fixation by immersion, fixation by perfusion caused a remarkable reduction in the number of light chief cells and atrophic cells, indicating that the occurrence of those kind of cells is dependent on factors of artifactual nature. The early response of the parathyroid gland to altered concentrations of extracellular calcium was studied in vitro. At six hours of "incubation, enlargement of the Golgi zone (Golgi complex and presecretory granules), but unaltered endoplasmic reticulum, was seen in glands incubated in low (0,5 mM) compared to those incubated in high (3,0 mM) calcium concentrations. Prolonged hypocalcemia induced in vivo by intraperitoneal injections of ethylenediaminetetraacetate and calcium deficient diet for eight days, did not give rise to any major quantitative morphological changes in the individual parathyroid cell, and furthermore, the quantitative morphology of the parathyroid cell was unchanged in experimentally induced hyperparathyroidism (calcium deficient diet for 16 weeks). The morphological data do not support the opinion of a functional cycle in the parathyroid chief cell, but suggest that the early response of this cell to altered extracellular calcium may be funtional activities associated with the Golgi zone. / <p>S. 1-48: sammanfattning, s. 49-170: 5 uppsatser</p> / digitalisering@umu