The analysis of pesticide residues presents unusual problems because of the small amounts of materials that must be measured and the large amounts of interfering substances that must be removed. In general, it is necessary to be able to analyze for pesticides at the 0.01 to 10 ppm level in foods and animal tissues and at the ppt or ppb levels and upward in environmental pollution studies. After the pesticide has been extracted from the sample and interfering compounds removed, the residue is ready for analysis. These are usually colorimetric tests that are based on causing the pesticide to react with a reagent to produce a chromophore. During the past ten years colorimetric methods have been gradually superseded by chromatographic procedures in which a number of pesticides can be analyzed in the same operation. Three forms of chromatography are currently in use: paper, thin-layer, and gas. The use of paper chromatography is declining while that of thinlayer chromatography is increasing. However, gas chromatography is superior to both of these methods with respect to resolution and sensitivity. Also the use of infrared spectroscopy was discussed.