Experiments on the control of larvae of Tabanus spp. in salt marshes with granular formulations of insecticide were made on Long Island, New York, in 1955 and 1956. In 1955, granules of Attaclay or Diluex impregnated with dieldrin, aldrin, chlordane, heptachlor or DDT were applied by hand to 60-ft. square plots in salt marshes having high and relatively uniform populations of Tabanus larvae. Granules were used because they readily penetrate the dense marsh vegetation. Results were evaluated by a method in which the larvae are brought to the surface of cleared areas by the use of a pyrethrum spray [see next abstract]. Dieldrin was applied at dosages of 0.09-2.5 lb. per acre and was the most effective of the insecticides tested [cf. R.A.E., B 45 116]. No larvae could be found in plots treated with the higher dosages (0.6 Ib. or more) after ten days, or in any of the plots after 32 days, when control plots yielded 14.9 larvae per sq. yard. DDT was the least effective insecticide, giving poor control in 28 days at 2 Ib. per acre. The addition of 5 per cent. urea as a stabiliser to granules of 30/40 mesh Attaclay with 2.5 per cent. dieldrin, which was tried in 1956. did not appear to influence effectiveness.