ABSTRACIA procedure was selected for the simultaneous extraction and purification of abscisic acid (ABA) and indoleacetic acid (IAA). Unnecessary steps were eliminated and an accumulation of aqueous phase was avoided. The superior performance of diethyl ether (compared to ethyl acetate) for bulk purification and the superior resolution provided by 250 millimeter columns packed with 5-micrometer spherical particles of strong anion exchanger and octadecylsilane (C18) greatly facilitated the purification of samples. A fixed-wavelength (254 nanometer) ultraviolet detector and a fluorescence detector connected in series on a high performance liquid chromatograph permitted nondestructive monitoring and measurement of ABA and IAA. Derivatization was not necessary for chromatography or for detection. Isocratic elution with simple mobile phases gave sharp peaks. A few simple precautions minimized losses. Recoveries through the entire procedure averaged about 75% for ABA and about 50% for IAA. Purifled ABA and IAA fractions were usually free of interfering contaminants. Identities were confirmed by gas chromatography-mass spectrometry.Poor recovery is a frequent problem with IAA determination because IAA is easily oxidized and is subject to photodecomposition (11,14). ABA is also somewhat labile, although not as labile as IAA. Because of variable losses during extraction and purification, the use of internal standards is essential for accurate quantification of ABA and IAA (4). trans-ABA has been used as an internal standard for the estimation of ABA (9, 19), but the acceptability of its use depends upon its absence from the tissue being analyzed and upon lack of interconversion of ABA and trans-ABA during the procedure. The use of radioactive ABA as an internal standard circumvents these potential problems. Indolebutyric acid has been used as an internal standard for IAA (5,19), but its value is questionable because of differences in partitioning and chromatographic behavior and possible differences in stability. Labeled IAA is preferable as an internal standard.HPLC and GLC are frequently used in the final stages of purification and for quantification of ABA and IAA. HPLC has advantages over GLC in quantification because UV and fluorescence detectors, used with HPLC, are nondestructive, and the entire sample can readily be collected for measurement of radioactive internal standards. Also, it is not necessary to form volatile derivatives (e.g. by methylation or silylation) for HPLC as it is for GLC. The UV detector, however, is not very specific and impurities are likely to interfere with quantification unless the sample is almost pure.The objectives of the work reported here were to select procedures that would (a) permit simultaneous extraction and purification of ABA and IAA, (b) provide purification sufficient that ABA could be quantified by UV absorbance and IAA could be quantified by natural fluorescence with the detectors connected in series on an HPLC, (c) give a high percentage recovery so that small amounts of ...