A rapid method for determination of glutaraldehyde (GA) is described based on formation of the GA-bisulfite complex followed by iodometric titration of unreacted bisulfite. A 1-ml aliquot of 2-6% GA is added to 20 ml of 0.25 M Na bisulfite. A reaction time of 5 min is allowed, and the solution is titrated with 0.1 M triiodide. Blanks are run in parallel with 1 ml water or buffer. The method gave precisions of 0.2% or better and was not affected by phosphate, phosphate-sucrose or cacodylate buffers or by glutaric acid. Pure GA was prepared by vacuum distillation, analyzed by combustion and used as a primary standard. Deterioration of GA in water and buffer was studied by ultraviolet spectrometry and bisulfite titration. Ultraviolet extinction coefficients proved to be strong functions of time, temperature and initial concentration so that Beer's law was not obeyed. Deterioration led to the formation of polymeric materials, first water-soluble and then, with increasing polymerization, insoluble. Polymerization was most easily followed by observing the disappearance of aldehyde groups titrimetrically, since interpretation of the ultraviolet absorbances at 235: 280 mµ was subject to a multitude of conditions. Polymerization was independent of light, oxygen or transition metal ions, and nearly independent of temperature between 1 and 25°C. Under the proper conditions a partial, but slow, reversal of polymerization could be obtained. Because of the somewhat erratic deterioration shown by GA, periodic determinations of titer are advised if reproducible fixation is desired.