A major factor in determining the carcinogenic potential of an agent is its identification as being carcinogenic. While this statement appears obvious and even redundant, identification of a car- cinogen is necessary but not sufficient for determining carcinogenic potential. Still, identifica- tion is the starting point and for this reason has received the most attention. Generally speaking, the various tests that have been applied to identifying agents with carcinogenic potential may be classified into several general areas. These are seen in Table 13.2. As noted in the table, the time involved in the assay has been arbitrarily separated into short, medium, and long. Short-term assays usually involve days to a few weeks for development of an end point; medium-term as- says require weeks to some months but much less than a year. Long-term bioassays usually in-volve 1¹⁄₂ to 2 years of treatment of animals with a test agent. Each of these general categories consists of specific methods, and each is considered in somewhat greater detail below.