Infrared lasers for medical applications were summarized in this review. CO₂ laser is the first infrared medical laser. Use of conventional medical lasers depends on absorption coefficient of water. Nd:YAG laser is used in coagulation surgery. Ho:AG laser is used to cut or vaporize tissue. Er:YAG laser is used in caries therapy because of its large absorption coefficient of water. Pulse lasers are used because less than 1 μsec pulse lasers induce less thermal effect than CW lasers. The medical applications of FELs have merits of wavelength selectivity and psec-nsec pulse structure. When the wavelength can be tuned to the vibrational mode, the infrared lasers will be widely used on biomedical field in the near future because the lasers can activate bindings between biomolecules directly.