The vascularity of 20 primary skin melanomas was assessed histologically. These cases were selected from patients with intermediate thickness melanomas (0.76-4.0 mm thick) treated surgically to provide two groups of ten patients. One group had no evidence of recurrence with a minimum follow-up of 9 years. The second group of ten patients developed locoregional or systemic metastasis under follow-up, and seven of these patients died of disseminated melanoma. Age, sex, Breslow's tumor thickness, and Clark's level of invasion were similar in the two groups. Vascular quantitation was carried out by image analysis after vascular definition by Ulex europaeus-I agglutinin staining. The percentage vascular area at the tumor base in the recurrence group was more than twice that in the recurrence-free group. This study suggests that increased vascularity at the tumor base may have prognostic significance in intermediate thickness melanomas.