A spectrophotometric method, based on the electronic absorption and second-derivative spectra of beef drip, has been developed to detect the amount of carbon monoxide bound to myoglobin in treated beef samples. The method has been validated following the criteria reported in the Eurachem guides. The limit of detection, equal to 0.14 μm, has been evaluated analysing ten blank samples, taking into account the mean concentration and the resulting standard deviations. The accuracy of the method has been studied in terms of trueness and precision; the first is expressed as per cent recovery (always exceeding 90%) and the second as relative standard deviation. The method is easy, rapid and allows one to determine qualitatively and quantitatively the CO concentration in the meat drip, by simply measuring in the UV–Vis spectrum of an unknown sample the absorbance values at three specific wavelengths: 423, 429 and 434 nm.