A thermal cycling device having a sample chamber whose temperature can be rapidly and accurately modulated over a range of temperatures needed to carry out a number of biological procedures, such a the DNA polymerase chain reaction. Biological samples are placed in glass microcapillary tubes and then located inside the sample chamber. A programmable controller regulates the temperature of the sample inside the sample chamber. Once a heating cycle is completed, the controller opens a door to the chamber for venting hot air out and cool ambient air is moved in. Temperature versus time profiles corresponding to optimum denaturation, annealing and elongation temperatures for amplification of DNA are achievable by the present invention.