A simple spectrophotometric method is developed for the quantitative determination of dequalinium chloride. The proposed method is based on the formation of a green coloured product due to interaction with 7,7′,8,8′-tetracyanoquinodi-methane (TCNQ) in alkaline medium. At the maximum absorption of 488 nm, Beer's law is adhered to over the 2–20 μg ml−1range. Results of analysis of dequalinium chloride by the proposed method agree well with those reported in B.P 1988. The method is simple and rapid since the product is measured directly in solution without extraction.