Use of quantitative methods in X-ray microanalysis of biological specimens has expanded the scope of this technique. Reliable quantitation in biological microanalysis is, however, not simple, and a number of difficulties are typical for biological specimens. The purpose of this tutorial is to signal problems in quantitative X-ray microanalysis of biological specimens and to discuss possible solutions. First of all, the instrumental configuration has to be optimized and the contribution of extraneous sources to the spectrum minimized. Contamination and mass loss during irradiation have to be reduced. After the spectrum is obtained, background subtraction and deconvolution routines are applied. The contribution of extraneous sources to the spectrum has to be accurately determined and subtracted from the initial spectrum. Standards have to be prepared that contain the elements of interest in a known amount and are homogeneous. The intensities in specimen and standard are then compared and corrections are applied to correct for differences in composition between specimen and standard that are relevant to the resulting X-ray spectrum. These corrections are relatively simple for thin specimens but may be more intricate for bulk specimens. It is then important to know under which conditions the quantitative procedure can be simplified.