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We have developed a model capable of predicting the performance characteristics of a wiretype Joule-Thomson mici-ocooler intended for use within a cryosurgical probe. Our objective was to he able to predict cold tip temperature, temperature distribution, and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated gas equations of state to account for changing gas properties due to heat transfer witlun the heat exchanger and expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisynimetric finite difference code allowed simulation of axial conduction. To validate simulation results, we have constructed and conducted experiments with two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel. The parameters of the experiment were used in the calculations. CO2 was used as the coolant gas for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. The temperature measurements show that the model was successfully able to predict the cold tip temperature to a good degree of accuracy and well represent the temperature distribution. For the all PEEK niicrocooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a tempel-ature drop of57 K and mass flow rate of 19.5 mg/s compared to measui-ed values of 63 K and 19.4 mg/s, therefo,-e, showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified. [ABSTRACT FROM AUTHOR]