Seven types of phosphine detector tubes were tested with five types of pumps for drawing gas samples through the tubes. The accuracy of measuring a known concentration of phosphine was tested to assess the effects of combining each tube with each of the five pumps. Wide variations in readings were obtained with many of the tube-pump combinations. Some tubes were more affected by varying rates of gas flow than others. The results reveal some of the limitations in using detector tubes for measuring phosphine concentrations, either in fumigation or for monitoring phosphine in air near fumigated material. -- CCI