Abstract: A block heating system includes a housing defining an open-top well closed at the bottom by a base plate which is heated by an electric heater in the housing. One or more carrier blocks are removably received in the well, each block having a plurality of receptacles in the top face for receiving test tubes or the like to be heated. A temperature probe assembly includes a rigid metal sheath projecting up into the well from the base plate and receivable in a bore in the bottom of one of the carrier blocks. A thermistor at the tip of the sheath senses the temperature in the middle of the block, which is displayed on an LED display on the front panel of the housing.