A sample of forty-nine 1975 and 1976 catalyst equipped vehicles operated in the Albany, New York area have been tested in “as received” condition for gaseous and particulate emissions at approximately 5,000 mile intervals. Each of the 127 tests includes a 1975 FTP, a one-hour 50 mph steady cruise, and five SET-7 (sulfate) cycles, all run on tank fuel. Test data includes HC, CO, NOx, SO2, idle HC and CO, soluble particulate sulfate, and fuel economy. Summaries of emission rates are presented as a function of catalyst type, manufacturer, and emission parameters. Specific attention is given to release of stored sulfur during idle periods between test driving modes. Data is also presented on plugged converters found on high mileage police vehicles. This serious plugging appears to be the result of deposition of manganese and oil additive related compounds in monolith cells on cars run of fuel containing MMT additive.