This paper reports on a study of the effects of a Tennessee law aimed at increasing the protection of children in cars. The law, which came into force January 1, 1978, requires parents to use child restraints properly when transporting their children who are less than 4 years old. Alternatively, the law permits children to be held in arms, a practice known to be hazardous rather than protective. Before and after the law went into force, observations were made of children in cars exiting from shopping centers in Knoxville and Nashville in Tennessee and in Lexington and Louisville in Kentucky, an adjacent state not having a child restraint law. More than 80% of Tennessee children observed in the fourth month the law was in force were not using child restraints anchored by seat belts, although use rates increased in Tennessee (8% to 16%) to a greater extent than in Kentucky (11% to 15%). Moreover, due to a large increase in children traveling in arms in Nashville, there was an increase in such travel in the two Tennessee cities studied (23% to 28%) relative to a decrease in those studied in Kentucky (19% to 14%). Despite results of the Tennessee law thus far, seat belt legislation based on scientific knowledge concerning crash protection is potentially important as a means of increasing the protection of children in cars, and should be encouraged. (Author/BD)