Our aim was to identify and delineate alterations in the distribution and immunophenotype of the lymphocytes and paracortical dendritic leucocytes (interdigitating dendritic cells; IDCs) in lymph nodes regional to tumours. Using immunocytochemistry and computer-assisted image analysis we examined 65 lymph nodes excised from 47 patients with malignant melanoma. Twenty-nine patients had American Joint Committee on Cancer (AJCC) stage II melanoma (no tumour spread beyond the primary site) and 18 had AJCC stage III disease (metastases in the regional nodes). There were significant differences in the frequency, morphology, immunophenotype and anatomical distribution of the IDCs and in the complexity of their dendritic processes in different areas within individual lymph nodes. We conclude that morphological and phenotypical variations in IDCs correlate with differing levels of antigen presentation. Downregulation of antigen presentation in lymph nodes regional to tumours is most probably mediated by tumour products. Differences in IDC distribution and characteristics in lymph nodes from different anatomical sites must be considered in interpreting studies of nodal morphology and function.