The state of collagen aggregation in hepatic granulomas produced in experimental murine schistosomiasis and harvested at different phases of the disease was estimated by staining histological sections in Picrosirius and studying them under polarized light. Two different types of collagenous fibres appeared successively during granuloma evolution, the first population, of thin, weakly birefringent, greenish fibres being replaced by thicker collagen fibres which display a stronger yellow-red birefringence. A simple morphometric technique (a point-counting procedure) was used to quantify the two distinct populations of collagenous fibres. Curve-fitting procedures were then employed, using the state of collagen aggregation as the dependent variable and time as the independent variable. The results showed that there is a progressive organization of the collagenous scaffolding of hepatic granulomas, such that quantitative study of the degree of collagen organization allows an adequate determination of the age of each granuloma. The combination of the Picrosirius-polarization method with simple and efficient morphometric approaches will clearly provide useful information on the natural history of schistosomal granuloma scarring.