A simple colorimetric assay method has been developed to quantify isoetharine hydrochloride in inhalation solutions. The method is based on a very simple reaction with potassium ferricyanide in a 0.05 M phosphate buffer solution. The color so developed can be measured at 500 nm. Beer's law was followed. The results were precise and accurate, with percent relative standard deviation of 0.6 based on 5 readings. The results using the developed method were in excellent agreement with the results obtained using the USP-NF method which is based on HPLC. Iodine solution was used to prevent the interference from the antioxidant (acetone sodium bisulfite). There was no interference from the other excipients present and from the two structurally related compounds, metaproterenol and terbutaline