ACENTURY AGO, when less than 1 percent of Americans smoked, few people worried about the health hazards of tobacco. But by 1950, with half of all Americans smoking regularly, concerns began to surface. In the 1960s, when scientists showed a connection between smoking and disease, the first warning labels appeared on cigarette packages: "CIGARETTE SMOKING MAY BE HAZARDOUS TO YOUR HEALTH."

Over the years, the warning labels became more forceful: "THE SURGEON GENERAL HAS DETERMINED THAT CIGARETTE SMOKING IS HAZARDOUS TO YOUR HEALTH." Since 1984, the warnings have clearly named the principal hazards of smoking: lung cancer, heart disease, emphysema, and complications in pregnancy. Every American-produced cigarette package and advertisement carries the notice "SMOKING CAUSES . . ." followed by the name of one of the conditions. Interestingly, the 1993 Gallup study on teen smoking showed that smokers have a greater recall than nonsmokers of the messages...