Form birefringence of collagen bundles and pure collagen I was measured, following immersion in water, glycerol solutions and nujol. No differences were found in the curves obtained for collagen bundles as compared to pure collagen I, the lowest optical retardation always corresponding to n=1, 46 (pure glycerol). However, when oil media were used, the values of optical retardation varied greatly. The main objective of this study is to show some advantages of the use of glycerol solutions as media for form birefringence measurement.