50 guinea pigs were allergized three times in 3 days intervals by subcutaneous injection of 25% solution of egg-white in physiological saline in a dose of 0-1 ml/100 g of body weight. On the 21 day after the last injection the animals were exposed to aerosol of antigen of egg-white. 11 animals died in acute anaphylactic shock. The control group consisted of 12 guinea pigs which received subcutaneously a solution of physiological sodium chloride of the same dosis--0-1 ml/100 g of body weight and were also exposed to the allergen, together with the experimental group. The removed parathyroids together with the thyroid gland were studied with histologic and cytoenzymatic methods. The activity of alkaline and acid phosphomonoesterase, nonspecific AS-naphtol acetate esterase, succinic (SDH), lactic (LDH) and D-L-alfaglicerophosphate dehydrogenase (alpha-GPD) were tested. No morphological changes in the parathyroids of guinea pigs in anaphylactic shock were found. Instead a decrease of the enzymatic activity of dehydrogenases was found, what might be connected with the decrease of metabolic activity of the cells. The decrease of alkaline phosphatase activity in the endothelial cells of the capillaries was another finding. It is likely that in an acute anaphylactic shock in guinea pigs only functional changes develop which have not counterparts in histology visible under the light microscope.