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Describes a system for thawing frozen cell suspensions and tissues by electromagnetic absorption. A 25-ml sample is heated in a cylindrical resonant cavity, which is excited in three modes all close to 434 MHz. Maximum warming rates are over 10°C/s (600 C/min), and a frozen sample may be brought from -65°C to room temperature in <30 s, with final spatial differences of <20°C. Samples may be frozen externally, or cooled within the cavity at typically 1°C/min. The authors have also used the resonant cavity to measure the permittivity and conductivity of the sample at temperatures from -83°C to +8°C. By measuring the heat capacity of the sample, the authors have calculated the power deposited in it as a function of its temperature. The system is currently being used to investigate the effect of warming rate on cell survival.