Abstract The expression of human leukocyte antigen-DR (HLA-DR) and β 2-microglobulin on the tumor cells and their correlation (if any) to the degree and the composition of the peritumoral mononuclear infiltrate were studied in 37 basal cell carcinomas from 32 patients with an indirect immunoperoxidase technique. In 36 of 37 basal cell carcinomas (97%) there was no expression of HLA-DR on tumor cells of basal cell carcinoma. In 13 of 37 basal cell carcinomas (35%) β 2-microglobulin was expressed on the tumor cells. Both a diffuse cytoplasmic and a membrane staining were observed in only six of these 13 basal cell carcinomas; in the other seven basal cell carcinomas only a diffuse cytoplasmic staining was observed. In all 37 basal cell carcinomas there was membrane staining for β 2-microglobulin in the normal epidermis. The intensity of staining in the normal epidermis was always stronger than that in the tumor nests. There was a varying degree of peritumoral immune infiltrate in all basal cell carcinomas. It comprised mainly T cells (mean percentage 57 ± 15). In the group of patients with basal cell carcinoma with moderate to heavy infiltrate the mean percentage of T cells was 63 ± 13, which was significantly higher than the mean percentage of T cells (46% ± 14%) in the group of patients with basal cell carcinoma with a mild infiltrate. This difference was mainly the result of an increase in T helper cells. The absence of HLA-DR or the decreased expression of β 2-microglobulin neither correlated with the degree nor the composition of the peritumoral infiltrate. From these results it can be concluded that despite the absence of HLA-DR and a decreased expression of β 2-microglobulin on tumor cells of basal cell carcinoma, a T cell-mediated immune response against basal cell carcinoma proliferation is evoked.