A simple and sensitive spectrophotometric method for the determination of traces of niobium(V) is based on the colour reaction between niobium(V) and phenylfluorone (Pfn) in the presence of Zephiramine micelles in dilute hydrochloric acid and extraction of the complex on a membrane filter. The absorbance of the Nb(V)-Pfn complex is measured directly on the filter. The detection limit is 4 ng for 30 ml of sample solution.