Rabbit psoas skeletal muscle fibers were held at constant length and rigor induced by immersion in 0.2% saponin. The fibers were quick-frozen by contact with a liquid helium-cooled copper block in a Heuser-type cryopress, and freeze-etched in a Balzers 400 freeze fracture machine. The sample was then rotary-replicated with Pt-C at 24 degrees and visualized in a JEOL 100CX2 transmission electron microscope operated at 100 kev. Images were recorded on Kodak 4489 film at 75,000x magnification. Stereo pairs were taken at +5 and -5 degrees. Films were scanned with a 20 micrometer pixel spacing on a Nikon Coolscan 9000ED scanner. Stereo pair with CIL:2879.