Abstract: A thermocouple, particularly for use in a gas turbine engine, comprises a mineral-insulated thermocouple element having its sensing end reduced in diameter by swaging, to increase sensitivity and reduce response time. Instead of swaging the whole sensing end to the reduced diameter, with a relatively large taper angle, typically about 14.degree., between the swaged and unswaged portions, the end is provided with a more gradual taper extending over substantially its whole length and having an inclusive taper angle of not more than 5.degree., and preferably about 21/2.degree..