Extracts were prepared from lichen planus lesions and from healthy epidermis of normal controls. Their effect on the migration and lymphocyte transformation of autologous leukocytes was studied. On the whole, the ranges of variation and mean values of the autologous leukocyte migration indices obtained in the presence of LP skin extract or sediment from 10 LP patients did not significantly differ from those recorded in the presence of similar extracts prepared from the epidermis of 12 normal controls. Two assays with LP skin sediment antigen and one assay with LP supernatant antigen, however, fell within the range of significant changes in migration. Lymphocyte transformation, as indicated by increased thymidine uptake, was significantly stimulated by LP epidermis in 1 case of 5 LP patients. Extracts from normal epidermis did not affect the transformation of autologous lymphocytes. The phytohemagglutinin response of lymphocytes from LP patients was the same as that of normal controls. The results do not indicate that cell-mediated immunity toward epidermal antigens play any significant role in the etiopathogenesis of lichen planus.