A point focus X-ray tube has been used as a source for microanalysis by the X-ray absorption method. Transmission measurements on selected specimen areas of 2-10 μ diameter are possible, with wavelengths chosen by a crystal and a proportional counter. Comparison of the transmitted intensities at different wavelengths gives quantitative information on the mass thickness of elements present in the area examined. The ultimate mass sensitivity varies with the position of the element in the periodic table but is usually in the range 10^-10-10^-12 g for elements of Z > 15. The application of the method to the determination of calcium is described.