The effect of operational parameters upon dustiness test results in the Heubach and Midwest Research Institute (MRI) dustiness tests was evaluated. In the Heubach test the flow rate, sampling time, and mass tested can be varied by the user. In the MRI dustiness test, the bulk density, sampling rate, sampling time, and vibrator intensity can be varied. The effect of flow rate and sampling time upon the Heubach dustiness tester was evaluated by varying the flow rate and conducting Heubach dustiness tests on 20 grams of limestone. The test was operated at flow rates of 5, 10, 15, and 20 liters/minute. The mass of the material tested affected the Heubach dustiness index. The relationship between the amount of mass collected and the dustiness index was not a simple linear relationship. To evaluate the effect of flow rate and sampling time on the MRI dustiness tester results, limestone was used to conduct MRI dustiness tests at flow rates of 5, 10, 19.6, and 27 liters/minute. Each of the tested parameters affected the amount of dust and the size distribution of the dust produced during the test. The authors recommend that for Heubach dustiness testing, airflow rate, sampling time, and mass of material tested be controlled. For the MRI dustiness tester, the user must strictly adhere to the test procedures.