Skin types 1 and 2, increased numbers of moles, and excessive intermittent sun exposure are known risk factors for cutaneous melanoma, but the inter-relationship between UV radiation exposure, moles and melanoma remains unclear. There is a noteworthy site variation in melanoma, it being more common on the lower leg in women and on the back in men. In order to determine whether this site variation could provide further clues to the pathogenesis of melanoma, we examined site variation in photosensitivity and its relationship to other known melanoma risk factors (number of moles, skin type and skin colour) in 25 healthy volunteers. A marked site variation in photosensitivity was found. The pale skin of the volar aspect of the forearm was markedly less photosensitive than the darker skin of the back. Females were more photoresistant than males on the lower legs even though this is the more common site for melanoma in women. There was some correlation between the number of moles and photosensitivity at the two sites.