Overexpression of proto-oncogenes (c-onc) may be involved in the initiation and progression of human neoplasia. We investigated the mRNA expression of the proto-oncogenes c-myc, c-fos, c-neu (erb B-2) and Ha-ras in 12 cutaneous melanocytic lesions (four dermal naevi, seven melanomas; one cutaneous metastatis of melanoma) and in normal skin (five cases) by Northern blot analysis; mRNA expression levels were quantified by densitometry of the specific bands. The expression of c-myc mRNA was higher in naevi than in melanomas, whereas c-fos mRNA expression was significantly higher in melanomas than in naevi. No significant differences were detected in the c-neu and Ha-ras mRNA levels in naevi and melanomas. The expression of c-neu mRNA was higher in normal skin than in the melanocytic lesions examined. Our results suggest that enhanced c-myc and c-fos expression may play an important role in the growth of melanocytic naevi and melanomas. The overexpression of c-fos may be involved in the progression of a particular subset of melanoma. Activation of Ha-ras and the c-neu gene, as determined by mRNA overexpression, does not seem to play a significant role in the progression of cutaneous pigmented lesions. Expression of c-neu may have an important function in the proliferation and/or differentiation of normal cells of the epidermis.