Shoulder belt use was observed before and after belt use laws went into effect in New York, New Jersey, Illinois, and Texas. There were large increases in belt use rates in each state in the first month the laws were enforced. In the three states in which post-law observations were made more than once, belt use declined from the levels seen in the first month; rates generally dropped to less than 50 percent. This pattern of decline from initial use rates has also been found in other jurisdictions around the world. Combined enforcement and publicity campaigns have been shown to be capable of reversing this trend and to increase use rates to 65 percent or more. Such campaigns will be needed to maximize the effect of seat belt use laws in the United States.