Chronologic and morphometric changes in the inferior olivary nucleus of the human medulla oblongata were studied in eight cases of primary pontine hemorrhage with different survival periods. To measure the olivary areas and analyze the neuronal and glial components, an optic electronic planimeter was used. A desk-top computer was also used for the calculation of the obtained data. The olivary enlargement was observed in cases with survival periods ranging from 3 weeks after the onset to 9.5 months. A morphometric analysis revealed six different stages of olivary changes after the destruction of the central tegmental tract in the pons: (1) no olivary changes, (2) olivary amiculum degeneration, (3) olivary hypertrophy, (4) culminant olivary enlargement, (5) olivary pseudohypertrophy, and (6) olivary atrophy. In stage (3) - noticed here for the first time -, neuronal cellular hypertrophy and sclerotic neurons with "insect-bite appearance" were observed. In stages (4) and (5), we also found the presence of prominent gemistocytic astrocytes in the characteristically enlarged inferior olivary nuclei. However, no proliferation of astrocytes during the olivary enlargement was confirmed in the morphometric analysis.