Collagen may be reprecipitated as obliquely striated fibrils. The oblique striations are due to D-periodic subfibrils staggered axially by approximately 9.0 nm with respect to their neighbours (Bruns, Trelstad & Gross 1973). The diameter of the subfibrils is variable. Optical diffraction analysis of the electron micrographs reveals instances of subfibrils with the D-repeat having diameter 3.7-4.0 nm. We argue that this structure is probably the five-stranded microfibril suggested by Smith (1968).