Chloroquine is a 4-aminoquinoline drug long used in the treatment or prevention of malaria. As it also mildly suppresses the immune system, it is used in some autoimmune disorders, such as rheumatoid arthritis and lupus erythematosus. After the malaria parasite Plasmodium falciparum started to develop widespread resistance to chloroquine, new potential utilisations of this cheap and widely available drug have been investigated. For example, chloroquine is in clinical trials as an investigational antiretroviral in humans with HIV-1/AIDS and as a potential antiviral agent against chikungunya fever. Moreover, the radiosensitizing and chemosensitizing properties of chloroquine are beginning to be exploited in anticancer strategies in humans.