Speciation analysis has been used for many years to identify and measure different forms of a given chemical in environmental and human samples. Although the term "speciation" is generally applied to the measurement of inorganic chemicals, the term can also be applied to many measurements of organic chemicals in complex samples, such as environmental media and biological matrices. We present several examples of achieving speciation analysis by selecting the appropriate biological matrix in which to measure a specific chemical(s), by a given analytical method, for the most accurate assessment of human exposure to the environmental chemical. Much of this information and many of these techniques are transferable to the measurement of inorganic elements in environmental and biological samples.