In a method of monitoring the operation of a plain bearing, a lubricant passage (15) of a bearing segment, this lubricating passage (15) being provided for jacking oil for example, is used during hydrodynamic operation of the plain bearing for extracting samples for a temperature measurement. For producing the measuring operation, a switch-over device (19) clears a flow path from the lubricant passage (15) into an outflow passage (23) in such a way that lubricant from the lubricating film (13) flows through the lubricant passage, the temperarature of this lubricant being determined by a temperature sensor (16, 18).