The present invention discloses a high temperature pyrometer 20 which is suitable, in particular, for temperature measurement in a gas turbine. The pyrometer comprises a flexible lightguiding measuring probe 21 with a microlens 22 resistant to high temperatures and with an optic fiber 24 composed of quartz or sapphire, said microlens and said fiber being provided with a gold sheathing 25, 26 and/or a protective capillary 27, 28. The heat radiation is evaluated in a remote detector 32 having measuring electronics 33 connected to it. The pyrometer 20 is distinguished by compactness, high temperature capability, flexibility, versatile installability and high measuring accuracy. The invention also relates to a development of the pyrometer 20 for gas turbines, to a gas turbine with a pyrometer 20 according to the invention, and to a method for monitoring a gas turbine with the aid of a pyrometer 20. Explanations are given of ways in which the measuring probe 21 can be fitted in guide blades 34, 48 and by means of which accurate temperature measurements are possible on moving and guide blades 34, 35, 48, 49 in low pressure and high pressure turbines. The operating safety and the efficiency of gas turbines can thereby be increased.