Tissues from 92 proliferative lesions of the melanocytic lineage defining distinct steps in tumour progression were investigated immunohistochemically for changes in angiogenesis, expression of fibroblast growth factor-2 (FGF-2) and density of total mast cells (MCs) and MCs expressing tryptase, an angiogenic-inducing molecule. Although the microvessel number was low in common nevi, it increased significantly in nevi with architectural disorder with varying degrees of melanocytic atypia (termed 'nevi with ADMA'), and these changes persisted during tumour development. Progression of primary melanomas was accompanied by a high microvessel number, and the progression to metastases by another significant increase in the microvessel counts. Expression of FGF-2, evaluated as percentages of positive lesions and positive cells per lesion was upregulated in the course of progression. Changes in expression were associated with nevi with ADMA, tumour changeover, penetration of the tumour into the dermis and metastases. A high correlation was demonstrated in all groups of tissues between the microvessel counts, percentages of FGF-2-positive tumour cells, and both total metachromatic and tryptase-reactive MCs. These results suggest that angiogenesis in human melanoma increases with tumour progression and that FGF-2 secreted by tumour cells and tryptase secreted by host MCs cooperate in its induction.