Fluorescent pigment in a self-marking device on a Malaise trap baited with CO2(released at rates of 100 or 500 ml/min) was used to estimate the size of the tabanid population in the Delta Experimental Forest, Stoneville, MS. The estimated daily average for the 1st test from August 1–25, 1974, was 989,195 ♀ tabanids in the 4-mile2(10.4 km2) area. The estimated daily average for a 2nd test from Sept. 10 to Oct. 7, 1974 was 275,497 ♀ tabanids in the same area.