Spitz naevi and halo naevi are benign melanocytic lesions that share many histological features with malignant melanoma. All lesions are characterized by a brisk infiltration of lymphocytes, mainly of the T cell subtype, and halo naevi are known to undergo spontaneous regression. Since the benign nature of Spitz naevi and halo naevi might therefore be caused by specific T cell responses against tumour-associated antigens, it was found of interest to characterize this T cell response in detail. A reverse transcriptase-polymerase chain reaction (RTPCR)- based method adapted for analysis of paraffin-embedded material combined with Southern blot analysis has been used to analyse the T cell receptor (TCR) AV and BV repertoires of infiltrating lymphocytes in 14 different melanocytic lesions. The results have shown that only a few particular TCRAV and TCRBV regions are expressed in each lesion. To evaluate the T cell response, it is of interest to know the HLA-type of the analysed lesions, since most melanoma-specific effector lymphocytes are CD8+ cytotoxic T cells and therefore HLA class l-restricted. As blood samples were not available from any of these patients, an RT-PCR method using HLA-A2-specific primers was used to analyse for the presence of this allele. The preferentially expressed TCRAV genes were sequenced, and this analysis showed that the high expression of these TCRAV genes was due to a clonal or oligoclonal expansion of T cells. In summary, the expression of relatively few TCR variable regions indicates a clonal expansion of T cells.