Nine cases of homogenous leukoplakia and 21 cases of lichen planus (11 reticular and 10 erosive) were studied under the scanning and transmission electron microscopes. Characteristic differences between leukoplakia and lichen planus in surface patterns of the epithelial surface cells were noted. Microridges in leukoplakia form parallel and anastomosing rows whereas the picture in lichen planus is irregular with microridges varying in width. The transmission electron microscopic findings confirm and correlate with these findings, the microridges representing invaginations of the plasma membrane. The keratin patterns exhibited by the surface cells were also characteristic regarding type and site of lesion. Scanning electron microscopy can be used as an additional diagnostic aid in differentiating these lesions.