Bloodletting was an archaic medical procedure in which blood was deliberately released from a patient in the belief that it would cure disease. The practice was usually abandoned upon advances in medicine.

In 2376, Abarca, a Qomar disdainful of the "primitive" technology of the USS Voyager, asked The Doctor whether his program included bloodletting. The Doctor replied that it didn't, but that he'd be "happy to add it to [his] repertoire." (VOY: "Virtuoso")

Kelis' people, a Bronze Age civilization, practiced bloodletting, which they believe released fever. (VOY: "Muse")