The two highest frequency measurements as yet reported are described. Frequencies of the 28‐ and 78‐&mgr;m cw water vapor laser lines were found to be 10.718073±0.000002 THz and 3.821775±0.000003 THz, respectively, by beating each of these radiations with the 337‐ and 373‐&mgr;m (0.89‐ and 0.80‐THz) radiation from an HCN laser, in a metal‐on‐metal point‐contact diode. The frequencies of the HCN laser were in turn measured by beating the 337‐&mgr;m radiation with 74‐GHz radiation and by measuring the 337‐ and 373‐&mgr;m frequency difference.