A study of the use of rollover protective structures (ROPS) on farm tractors was conducted. The purpose of this study was to obtain a better understanding of the ROPS issue in the US and to try to determine as accurately as possible the cost of retrofitting tractors with ROPS. Data on the prevalence of ROPS use on farm tractors, the age of farm tractors and the types of farming operations that used tractors, and the most common makes and models of farm tractors in use were obtained from a postal questionnaire sent to 25,200 agricultural production operations in 21 states. The costs of retrofitting the tractors were estimated using information from a publication of the Wisconsin Rural Health Research Center. Usable responses were received from 12,913 farming operations. There were 28,542 tractors being used on the farms. The use of ROPS on the tractors varied from 31.9% for tractors used in vegetable, fruit, or nut production to 48% for tractors used on cash grain farms. When projected to a national level, the data indicated that 4,800,000 tractors were being used in the US in 1993. Their average age was 22.8 years. Approximately 2,976,000 tractors (62%) did not have ROPS or cabs. Of the remaining tractors, 547,200 had ROPS and 1,276,800 had cabs. Tractors over 20 years of age were less likely to be fitted with ROPS than newer tractors. Projections for the future indicated that if 1,302,000 of the tractors were retrofitted with ROPS, 1,478 lives would be saved over the next 10 to 20 years, assuming a fatality rate of 57.1 deaths per 200,000,00 hours of unprotected tractor use. The estimated cost per life saved for retrofitting with ROPS would be 824,500 dollars. On a per tractor basis, this would be 937 dollars. The authors conclude that the large number of tractors on US farms that do not have ROPS represents a major public health problem. Suggestions for increasing ROPS use on farm tractors were presented.