Morphological lesions in parenchimal and mesenchimal structures of liver and kidney were studied in guinea-pigs experimentally infected with Leptospira interrogans serogroup icterohaemorrhagiae in comparison with a group of non-infected guinea-pigs. All specimens were submitted to conventional light microscopy as well as to high resolution light microscopy, in one micrometer sections of tissue embedded in glycolmethacrylate. High resolution light microscopy, applied for the first time in leptospirosis, was proved very useful, since it enabled us to visualize cellular structures in the same slide used for panoramic view. Cell cohesion, brush borders, pynocytotic vesicles and organellae distributions were parameters especially suitable for analysis at this low-cost, highly precise procedure in microscopy.