At the 1965 SAE Mid-Year Meeting in Chicago, fleet operators commented on hydraulic brake tube failures. Since little factual information was available on the effects of service life on the performance of hydraulic brake lines, a program was initiated to obtain this information. Results of the program indicate that corrosive deterioration of the steel hydraulic brake tubing now being used on cars and trucks creates maintenance problems and can be a safety hazard. The investigation also showed that the performance of presently used brake tubing becomes highly erratic after four to six years in service.Age of the vehicle appears to be more significant than mileage relative to brake tube corrosion. However, there are so many variables which influence brake line corrosion that attempts to correlate the results of the investigation with any one factor, such as age, are difficult. The investigation also established that the appearance of brake tubing does not always give an accurate indication of its performance.