An apparatus for processing biological samples comprising means for processing at least one biological sample accommodated on at least one carrier member in a chamber, wherein the apparatus comprises: a bottom member of the chamber, which bottom member is configured to support the at least one biological sample accommodated on the at least one carrier member; and at least one reservoir able to adsorb and/or absorb and desorb and/or release water, which at least one reservoir is disposed inside the chamber; and wherein the apparatus is characterized by: a lid for the chamber, to which lid the at least one reservoir is attached and that in a closed position is configured to cover the at least one sample such that the at least one reservoir does not touch the at least one biological sample on the at least one carrier member, and wherein the bottom member includes a temperature controlled heating plate for controlling the temperature of the carrier member and of the at least one biological sample on the carrier member, said heating plate is arranged below the at least one carrier member, wherein the at least one reservoir either absorbs or desorbs water and water vapor so as to control relative humidity within the closed chamber at at least 80% relative humidity, when the lid is positioned in the closed position, and wherein the reservoir is a device made of a material having a high internal surface area for absorbing and desorbing the water and water vapor. a bottom member of the chamber, which bottom member is configured to support the at least one biological sample accommodated on the at least one carrier member; and at least one reservoir able to adsorb and/or absorb and desorb and/or release water, which at least one reservoir is disposed inside the chamber; and wherein the apparatus is characterized by: a lid for the chamber, to which lid the at least one reservoir is attached and that in a closed position is configured to cover the at least one sample such that the at least one reservoir does not touch the at least one biological sample on the at least one carrier member, and wherein the bottom member includes a temperature controlled heating plate for controlling the temperature of the carrier member and of the at least one biological sample on the carrier member, said heating plate is arranged below the at least one carrier member, wherein the at least one reservoir either absorbs or desorbs water and water vapor so as to control relative humidity within the closed chamber at at least 80% relative humidity, when the lid is positioned in the closed position, and wherein the reservoir is a device made of a material having a high internal surface area for absorbing and desorbing the water and water vapor. a lid for the chamber, to which lid the at least one reservoir is attached and that in a closed position is configured to cover the at least one sample such that the at least one reservoir does not touch the at least one biological sample on the at least one carrier member, and wherein the bottom member includes a temperature controlled heating plate for controlling the temperature of the carrier member and of the at least one biological sample on the carrier member, said heating plate is arranged below the at least one carrier member, wherein the at least one reservoir either absorbs or desorbs water and water vapor so as to control relative humidity within the closed chamber at at least 80% relative humidity, when the lid is positioned in the closed position, and wherein the reservoir is a device made of a material having a high internal surface area for absorbing and desorbing the water and water vapor.