The history (especially association with rodents or other animals) and physical exam (present of pox lesions) is presumptive evidence for a diagnosis of monkeypox. Caution is advised. Infectious-disease consultants and CDC personnel should be notified because this infection may represent two additional problems. First, in the U.S. or other countries, it may likely indicate an outbreak of monkeypox, and informed health authorities may help to identify the source of the infection and prevent its spread. The second problem is unlikely but far more serious; the early symptoms may represent a biological warfare or terrorist attack with smallpox that is mistakenly identified as monkeypox. Consequently, definitive diagnosis of this viral disease, outside of Africa, and especially in developed countries where monkeypox is not endemic, is urged. Most laboratories do not have the reagents to do this testing, so state labs or the CDC will need to process the samples to establish a definitive diagnosis. These tests are based on detecting antigenic structures (usually from skin or pox samples or occasionally serum) specific to either monkeypox virus or immunoglobulin that reacts with the virus. PCR (polymerase chain reaction), ELISA techniques (enzyme-linked immunosorbent assay), or Western blotting tests (immunoblotting) are the main tests used.