The invention relates to a laboratory apparatus, in particular for performing a polymerase chain reaction (PCR) in a plurality of PCR-samples, which comprises an arrangement for tempering samples, the arrangement comprising a tempering block for the tempering of samples, the tempering block comprising a reception side, which provides receptacles for receiving sample vessels, and a contact side for the contact of at least one tempering device, at least one tempering device, arranged in an area of said contact side, a pressure device, which comprises a pressure element and an auxiliary element, said at least one tempering device being arranged between said auxiliary element and the tempering block, the pressure element being linked to said auxiliary element and to the tempering block, and being arranged to press said at least one tempering device against the tempering block by pressing said auxiliary element against said at least one tempering device, wherein at least one tempering device is shaped and arranged in said area to at least partially surround by itself said pressure element.