In order to apply the osmotic stress method for direct measurement of forces between membranes or between macromolecules, we have designed and built an x‐ray camera which can control the sample temperature from 0 °C to 70 °C while confining the path of diffracted x rays to an evacuated space between the sample and film. The system uses a linear feedback sensor which provides ±0.1 °C accuracy and a base‐line stability of 0.02 °C over the entire operating range. The controller uses solid‐state thermoelectric modules to regulate the temperature of the sample and is capable of automatically shifting from the heating to cooling mode of operation to regulate at temperatures near room temperature. The sample solutions are mounted between two Mylar windows in a removable cell which can be cleaned and loaded outside the instrument. The film plate is mounted on a slide which can be positioned between 4 and 22 in. from the sample. A beam stop is also mounted on the film plate holder and can be adjusted 1 in. both vertically and laterally. The x‐ray entry port also has lateral and vertical adjustments for easy alignment with the collimator. The sample cell and film plate mechanism are located within an aluminum and polycarbonate chamber for operation at pressures as low as 0.001 atm.