The present paper deals with the chemiluminescent determination of the herbicide Karbutilate on the basis of its previous photodegradation by using a low-pressure Hg lamp as UV source in a continuous-flow multicommutation assembly (a solenoid valves set). The pesticide solution was segmented by a solenoid valve and sequentially alternated with segments of the 0.001 mol l(-1) of NaOH solution, the suitable media for the formation of photo-fragments; then it passes through the photo-reactor and was lead to the flow-cell after being divided in small segments which were sequentially alternated with the oxidizing system; 2 x 10(-5) mol l(-1) of potassium permanganate in 0.2% pyrophosphoric acid. The studied calibration range, from 0.1 microg l(-1) to 65 mg l(-1), resulted in a linear behaviour over the range 20 microg l(-1)-20 mg l(-1) and fitting the linear equation: I=(1180+/-30)C+(15+/-5) with the correlation coefficient 0.9998. The limit of detection was 10 microg l(-1) and the sample throughput 17 h(-1). After testing the influence of a large series of potential interfering species, the method was applied to water and human urine samples.