A method for the measurement of a potential diuretic-antihypertensive agent, (+/-)-[[6,7-dichloro-2-(4-fluorophenyl)-2-methyl-1-oxo-5-indanyl] oxy]acetic acid, in biological fluids is described. The procedure involves the addition of a related internal standard to the specimens followed by extraction of the acids into toluene at pH 1. The indanyloxyacetic acids, following back-extraction into base and reextraction into methylene chloride at an acidic pH, are converted to methyl esters by reaction with ethereal diazomethane for subsequent gas chromatographic analysis. The sensitivity of the method is such that 5 ng of drug in 1 mL of biological specimen can be quantitated using a 63Ni electron-capture detector. The recovery from plasma in the 5-2000-ng/mL range (n = 53) was 97.0 +/- 16.3%. Differences were noted in the disposition of the enantiomers of this agent in dogs following a pharmacologically active dose.