This work was designed to verify if a simple quantitative procedure to estimate the state of collagen aggregation is useful in describing the natural history of a fibrous process. For this purpose sixteen cases of Lechiguana lesion were used. Histochemical evaluation of the collagen content and its state of aggregation was done by the Picrosirius-polarization method. Morphometric studies were done by means of a point-counting procedure, which allowed the determination of the areal fraction of thin and thick collagenous fibers within Lechiguana lesions collected at different times of clinical evolution (14 days through 8 months). Early lesions are characterized by thin collagenous fibers. This population of slender fibers decreases later on, when thick fibers become more prevalent. Curve fitting procedures were employed using the state of collagen aggregation as the dependent variable and time as the independent variable. The best fitting was obtained by linear and exponential functions. Statistical analysis indicates that the quantitative study of the degree of collagen organization allows an adequate determination of the time course of Lechiguana lesions. We concluded that simple determinations of collagen aggregation provide numerical data that may be useful to build mathematical models relating time of evolution of the disease to fibrosis.