Convoluted, stacked membranes in parallel or concentric array in the cells of a human meningioma consisted of closely arranged endoplasmic reticulum, usually devoid of ribosomes. The intercisternal space, about 280 Å in total width, was moderately dense and continuous with the cytoplasm at the periphery. The apposed cisternal membranes exhibited specialized intercisternal attachments appearing as three different structures, depending on the plane of section. Firstly dense particles bisecting the intercisternal space. They were 60 Å in diameter and 100 Å apart, being separate from each other and from the cisternal membranes. Secondly, a linear, sometimes beaded structure parallel to the cisternal membranes and bisecting the intercisternal space. Thirdly, bridge-like structures crossing the intercisternal space at 100 Å intervals appeared only in oblique sections of the closely packed endoplasmic reticulum.