Purpose. To evaluate the effects of low-dose UVB irradiation of HLA and CDla expression and the toxic effects of UVB on human corneas.Methods. 24 pairs of human corneas from 24 donors were studied. One cornea from each pair was randomly irradiated with UVB (100 mJ/cm2) after enucleation. All corneas were then organ-cultured for 2, 7, 14 or 21 days. Endothelium was studied after enucleation and organ culture. Following preservation, corneas were evaluated by means of light microscopy, morphometry and TEM. HLA and CDla staining was performed using an immuno-alkaline-phosphatase technique.Results. Endothelial cell loss during organ culture averaged 9.1% in the UVB group and 9.2% in the control group (NS). The number of rosette and reformation figures (p = 0.004) and the coefficient of variation (p = 0.014) were higher in the control group. Epithelial sloughing was more accentuated in the UVB group. We observed the same moderate ultrastructural injuries in both groups. In the epithelium, the average number of HLA-DR + cells per field was 0.12 in the UVB group and 0.42 in the control group (p = 0.035). In the stroma, these figures were respectively 1.04 and 1.34 (p = 0.026). In the epithelium, the average number of CDla + cells was respectively 0.025 and 0.078 (p = 0.019). In the preservation mediums, the average percentage of CDla + cells was 0.07% in the UVB group and 0.27% in the control group (p = 0.014).Conclusions. Low-dose UVB (100 mJ/cm2) decreases HLA-DR and CDla expression of organ-cultured human corneas and induces moderate corneal injuries. Low-dose UVB might be useful for preventing allograft rejection.