Energy-dispersive X-ray microanalysis (EDX) interfaced to a scanning/transmission electron microscope allows direct visualization and photographing of structures analyzed under the electron beam. EDX can perform a point-by-point analysis as it searches for the ion whose X-ray window the computer has been instructed to localize. This technique has been utilized to define ultrastructural immunogold labeling patterns. Once a specimen is immunolabeled with gold, microanalytical techniques can identify the quantity and distribution of detected and labeled antigenic epitopes. Microanalytical techniques add a new objective dimension to ultrastructural gold labeling procedures. Quantitative microanalysis of the gold-labeled antigenic sites provides a way of assessing the specificity of the reactions and permits comparison of the degree of expression of antigenic determinants in different specimens. Image processing allows visual representation of the immunolabeling results. Furthermore, statistical analysis of a large number of parameters is also possible with the digitized images collected. Ultrastructural microanalytical techniques represent a new, unexplored application that may play an important role in the future of ultrastructural pathology and immunologic evaluation of diseased tissues.