Tissue samples of parathyroid glands obtained from cattle, sheep and goat were immersed in either 2.5% glutaraldehyde (GA), or in 1% glutaraldehyde and 2% formaldehyde (FA) followed by immersion in 1% osmium tet-roxide (OsÖ4). The effect of different buffers used for aldehydes and osmium tetroxide respectively, were tested in order to determine the optimal conditions for preservation of parathyroid cell morphology. Uniform (the subcellular components of these cells showed no damage due to fixation), light (light cytoplasmic matrix and the subcellular components were damaged to a variable extent due to fixation) and dark (dark cytoplasmic matrix and shrunken cell) cells were found in the parathyroid tissues of all animals. Parathyroid tissue fixed with aldehydes in the presence of NaK-phosphate, Na-cacodylate or Hepes [4-(2-Hydroxyethyl)-1-Piperazinethan-Sulfonic acid] (with or without Ca2+ and Mg2+), and with osmium tetroxide in Na/K-phosphate or Na-cacodylate contained predominantly uniform. few light and dark cells. However, number of light cells Increased in parathyroid tissue fixed with osmium tetroxide in Hepes. In addition to the increased light cells, number of multinuclear cells (the cells contained fragments of the plasma membrane and markedly dilated cisternae of the rough endoplasmic reticulum) also increased in parathyroid tissues of sheep. The structure is better preserved and particularly the membranes are better visible in preparations fixed with a mixture of glutaraldehyde and formaldehyde than in those immersed only in glutaraldehyde. lt is concluded that the appearance of four different cell types depended to a great extent on the buffers and / or fixatives used in the experiment. lt is also concludet that buffers played more important roles then fixatives in the occurrence of these cell types.