Frozen hydrated sections of vitrified unstained insect flight muscle in the rigor and relaxed states were studied by cryo-electron microscopy. High resolution images with good contrast were obtained. As judged from direct images and from the comparison of optical diffractograms with X-ray diffraction patterns obtained from glycerinated muscle fibres, the vitrified specimen is well preserved. Preparation artifacts encountered in conventional plastic sections are avoided. The preservation of the relaxed structure also seems better than in freeze-etched replicas as the 14.5 nm repeat of crossbridges on thick filaments is easily visible.