The requirement by a producer or manufacturer that the purchaser of his product may not resell it to certain classes of purchasers is by now recognized as a serious restriction on freedom of trade and competition which the antitrust laws are meant to preserve. See White Motor Co. v. United States, 372 U.S. 253, 83 S.Ct. 696, 9 L.Ed.2d 738 (1963) In some cases such a restriction is deemed illegal per se, see United States v. Arnold, Schwinn & Co., 388 U.S. 365, 87 S.Ct. 1866, 18 L.Ed.2d 1249 (1967), and in others the rule of reason applies, see Janel Sales Corp. v. Lanvin Parfums, Inc., 396 F.2d 398 (2 Cir.), cert. denied 393 U.S. 938, 89 S.Ct. 303, 21 L.Ed.2d 275 (1968), requiring a knowledge of all the surrounding circumstances which reveal the practical effect and meaning of the restriction. Even if defendant's claim that it imposed the restriction on resale out of concern for the safety of the consumer were enough to take it out of the per se rule of Schwinn, the self-serving statements by lay businessmen of self-evident possibilities of harm are inadequate to prevent a trial of the issue under the rule of reason. We have before us no scientific or other expert testimony describing the nature or extent of the danger to laymen from the use of any of defendant's products, nor of any experience in the use of similar products containing adequate notice or warning. Information of this kind goes to the heart of plaintiff's case. For plaintiff has not claimed that there may be no danger whatever from the use of some of the defendant's products. Its claim instead is that whatever danger there is constitutes a risk which can reasonably be guarded against by labeling or even by individual cautionary advice. The effectiveness of this depends to a large extent, of course, on the nature of the risk and of the means which must be taken to guard against its potential harm.