A method to determine the proportions of the major fiber-forming collagens (types I, III, and V) in noncartilaginous human tissues is presented. The procedure relies on direct solubilization of tissue collagen as cyanogen bromide peptides. The peptides are subjected to cation exchange chromatography followed by gel permeation chromatography in a manner consistent with the rapid resolution and quantitation of relatively low-molecular-weight marker peptides for each collagen. The marker peptides utilized for type I, III, and V collagens are alpha 1 (I)-CB2, alpha 1 (III)-CB2, and alpha 1 (V)-CB1, respectively. Quantitation of the peptides is attained as a function of ultraviolet absorbance during gel permeation chromatography. The nature of the marker peptides, the use of high-performance liquid chromatography techniques, and quantitation of the peptides by ultraviolet absorbance renders the method suitably rapid, sensitive, and accurate for routine evaluations of collagen composition. The utility of the method is illustrated in the presentation of analyses on specimens of placental membranes and blood vessel walls.