Abstract: Apparatus for repeated automatic execution of a thermal cycle for the treatment of a sample, especially a biological sample, comprises means (6) defining a pathway which is physically closed throughout the treatment and within which the sample is resident throughout the treatment. Means (3, 4, 11, 12) are provided to move the sample between different positions along the pathway and (7, 15, 16) to heat or cool the sample as a function of its position within the pathway. Preferably the pathway is a capillary tube, which may be in spiral, closed loop or linear form. Heating and cooling means are provided by thermostated zones which may provide a continuous thermal gradient regular or irregular, or be in a discontinuous arrangement. The preferred means of moving the samples is magnetic.