A sensitive colorimetric method for the determination of zirconium has been developed for use in organic extracts which contain tri-n-octylphosphine oxide (TOPO) in cyclohexane. The method is based on the absorbance of the zirconium-pyrocatechol violet complex in a TOPO-cyclohexane-ethyl alcohol medium at a wavelength of 655 mμ. The molar absorbance index for this complex at 655 mμ is about 40,000. The complex conforms to Beer's law up to a concentration of 1.0 μg of zirconium per ml. When zirconium is extracted from a chloride medium, this method is useful for the determination of zirconium in the presence of large amounts of aluminium, uranium, vanadium, iron, and chromium; moderate amounts of thorium do not interfere. Molybdenum, titanium, and hafnium interfere with the method. The procedure is applicable in the presence of milligram amounts of phosphate and sulphate ion. When zirconium is extracted from a nitrate medium, the method is useful for the determination of zirconium in the presence of aluminium, titanium, molybdenum, vanadium, iron and chromium; however, uranium, thorium, and hafnium interfere. Microgram amounts of phosphate and sulphate ion can be tolerated. This method has the common advantage of most extraction methods in that zirconium which is present in an aqueous sample can be extracted into a smaller organic volume. The coefficient of variation for the determination of zirconium by this method is less than 3%.