Iris specimens obtained during the peripheral iridectomy in 12 cases (18 eyes) of primary angle closure glaucoma were studied histologically. The iris specimens taken during the senile cataract extraction in otherwise normal eyes were used as controls. The remarkable differences of the two groups are the changes of the quality and quantity of the mitochondria in the cells of iris tissue. The changes in primary glaucoma, especially in the intermittent stage of the angle closure glaucoma, were found in the mitochondria of the cells.