Cooling tower drift is defined as the percent of circulating water flow that exits from the cooling tower fan stack in the form of fine water droplets and aerosols entrained in the exhaust air. For cooling tower drift tests, the CTI recommended heated Bead Isokinetic (HBIK) procedure is the most commonly used procedure and is close to being accepted as a code by CTI, whereas regulators prefer the EPA Method 13A procedure. In theory both procedures (if properly operated, recovered and analyzed), should give the same results. This paper examines and compares the two-isokinetic methods and their proper operation, recovery and analysis so as to obtain accurate and repeatable results. The testing services of Midwest Research Institute (MRI) were retained by Brentwood Industries, Inc. to conduct a series of 18 drift tests by using both the CTI recommended HBIK drift test procedure and the EPA Method 13A drift test procedure. The tests were conducted simultaneously using both test procedures on two types of Brentwood drift eliminators at two water loadings and several air velocities at the Ceramic Cooling Tower Company's test facility located in Fort Worth, Texas. The drift from the test cell was determined by isokinetically sampling a representative fraction of the test cell airflow above the drift eliminators. Lithium was added to the test cell circulating water prior to starting the series of tests to serve as an analysis tracer. Inductively coupled argon plasma spectroscopy (ICP), an extremely sensitive detection technique, was then used to measure the concentration of lithium in the circulating water and in the collected drift samples. The total drift rates were calculated from the ratio of the concentration of the lithium in the sampling train to the concentration of the lithium in the circulating water. The CTI HBIK and the EPA 13A methods of isokinetic drift collection were found to yield nearly identical results in the series of tests.