The nonmelanoma skin cancers squamous cell carcinomas (SCC) and basal cell carcinomas (BCC) are by far the most common malignancies that occur in the United States each year. The third most common skin cancer, malignant melanomas (MM), accounted for 3% of all reportable cancers in the United States in 1991. The incidence of and mortality due to MM have been increasing at an alarming rate over at least the past 4 decades. As a result of this epidemic, there have been intense efforts to develop appropriate experimental models to examine the etiology and biology of this cancer. Benign and malignant melanocytic tumors have been produced in dogs, mice, guinea pigs, hamsters and gerbils with chemical carcinogens such as 7,12 dimethyl(a)benzanthracene (DMBA) and chemical promoters. Perhaps the most extensive and thorough studies using these chemicals were accomplished in the Weiser-Maple guinea pig model, in which radial and vertical stage growth occurred similar to human MM growth patterns. However, such stimuli are unlikely to be related to the human experience. Many investigators have considered ultraviolet radiation (UVR) from the sun to be intimately involved with the melanoma epidemic. Thus, a number of models have been developed to examine this possible relationship. These have included irradiation of DMBA-induced benign melanocytic tumors in pigmented hairless mice, chemical promotion of UVR-induced tumors in haired mice and the induction of melanomas by UVR in the South American opossum. In addition, a melanocytic growth was produced with psoralens plus UVA in a haired mouse. All of these melanomas required chronic UVR exposure.(ABSTRACT TRUNCATED AT 250 WORDS)