Functional studies have shown that the sphingolipid ceramide, self-assembles in

phospholipid membranes to form large channels capable of allowing proteins to cross the

membrane. Here these channels are visualized by negative stain transmission electron

microscopy. The images contain features consistent with stain-filled pores having a

roughly circular profile. There is no indication of tilt, and the results are consistent with

the formation of right cylinders. The sizes of the pores range from 5 to 40 nm in diameter

with an asymmetric distribution indicating no apparent upper size limit. The size

distribution matches well with the distribution of sizes calculated from

electrophysiological measurements.