When liquid ESMP and Mylanta II are compared in vitro, ESMP has a higher ANC rating; when they are compared in tablet form, Mylanta II’s ANC rating is higher. However, in vivo tests, conducted by both parties to demonstrate the relative effectiveness of the two brands of antacid, show no advantage for either brand in the human body. The district court found that “[n]ot one of the in vivo studies, performed by either side, demonstrated any statistically or clinically significant difference in the ability of Mylanta II or ESMP to relieve symptoms of acid indigestion.”
*128 The district court’s conclusion that neither in vitro nor in vivo tests provides any basis for either antacid manufacturer to claim that its product is more effective at relieving symptoms is well supported, and neither party contests it. The dispute is over whether Rorer caused consumers to think that ESMP was more effective at relieving symptoms by making misleading claims of superior relief in its commercials, thereby violating the Lanham Act.