Aerial spraying of a 0.9 mile section of the Patuxent River, Maryland, with DDT at 2 lbs. per acre, was followed by a recorded loss of 139 fish within 4 days. Minnows were affected before Lepomis macrochirus, Huro salmoides, and Schilboedes insignis. 69% of all dead fish were found 9.5 hrs. after spraying. In live-boxes stocked with equal numbers of L. macrochirus, L. auritus, and Perca flavescens, 79-97% of bluegills were killed, but mortality in yellow perch did not exceed 10%. Ash Creek, Pennsylvania, was sprayed by plane at 1 lb. DDT per acre with an estimated loss of 1.3% of the brook trout population. In 4 trout raceways at Leetown, West Virginia, 100 each of brook and rainbow trout, and of bluegill sunfish in each pond were exposed to a 1 lb. per acre treatment without the loss of a single trout, but 4-12% of bluegill sunfish were killed. 12 warm-water ponds at Leetown were stocked with 50 large fingerling bluegills and 50 large finger ling largemouth bass. Nine ponds were sprayed at 1 lb. DDT per acre in 3 different carriers. In ponds treated with DDT in xylene and fuel oil, 50-60% of bluegills were killed, but few bass were lost. An emulsion formula killed all fish, but a suspension formula killed only a few fish in one of 3 ponds. Houseflies sprayed at a 1 lb. per acre rate of DDT did not kill bluegills when fed to them in large numbers.