In order to determine the effects of the loss or reduced expression of molecules associated with antigen presentation (transporter associated with antigen presentation [TAP]-1, TAP-2, low molecular weight protein [LMP]-2 and LMP-7), we examined the expression of these molecules in primary uveal melanoma lesions. Paraffin-embedded sections from 29 primary uveal melanoma lesions were analysed for expression of TAP-1, TAP-2, LMP-2 and LMP-7 using specific primary antibodies followed by a three-stage immunoperoxidase technique. Microscopic examination was undertaken to determine differences in expression of these molecules on the tumour and the surrounding stroma. Overall, 72% (21 out of 29) of the tumours showed some loss or reduced expression of TAP-1, TAP-2, LMP-2 and/or LMP-7. Statistical analysis of these results showed that progression to metastatic disease was strongly associated with reduced expression of TAP-1 (P < 0.05) and TAP-2 (P < 0.01), taking patient age, tumour site and histology into account. We conclude that the reduced expression of molecules important in eliciting an immune response, such as TAP-1 and TAP-2, may facilitate the metastatic spread of uveal melanoma lesions and may have important implications for prospective immunotherapy.