Accuracy in trace organic analysis presents a formidable problem to the residue chemist. He is confronted with the analysis of a large number and variety of compounds present in a multiplicity of substrates at levels as low as parts-per-trillion. At these levels, collection, isolation, identification and quantification are all very difficult. Sample contamination and substrate interferences can also lead to large errors. Obtaining accurate qualitative data is often more of a problem than accuracy of quantitative data. Retention times and peak height measurements from gas chromatography coupled with highly sensitive, but nonspecific, detectors are most commonly used in residue analysis. Although dual column and/or dual detector determination, partition values and chemical derivatization are often employed, lack of good reference standards, interferences and poor detector specificity frequently cast doubt on the qualitative and quantitative accuracy of data upon which regulatory decisions may be made. Mass spectrometry and Fourier transform spectrophotometry offer partial solutions to qualitative accuracy where this instrumentation is available. However, less expensive and more sensitive specific detectors for gas chromatography are most needed. Means of quantitating residues from mixtures like polychlorobiphenyls and toxaphenes are far from adequate. Collection systems for environmental media often lack efficiency, especially for volatile organic compounds in air.