Two-dimensional (2-D) Fourier analysis was used to quantify the structural organization of collagen fibers in the dermis of the human skin. The 2-D Fourier spectra of electron micrographs of collagen fibers contained large amplitude Fourier components (1 fundamental and 3 harmonic peaks), representing the predominant structural parameter of the fibers, the center-to-center spacing of collagen fibrils. The average center-to-center spacing of the collagen fibrils was found from the position of the peaks. For a normal fiber of reticular dermis, this spacing was 116 nm. The fibril diameter appeared to modulate the peak heights.