The optical constants of liquid silver have been measured in the infra-red between wave numbers 4000 and 17000 cm−1. The results are compared with the Drude theory and lead to a value of about 1.1 for the effective number of free electrons per atom. The electrical conductivity of the surface layer, calculated from optical constants, differs by less than 10% from the bulk conductivity. Some results on the temperature variation of the optical constants are presented. The optical constants of liquid copper have also been measured at two wave numbers in the infra-red.