This report describes the results of a project in which pairs of tests were conducted in 84 in-use passenger cars, once under low temperature conditions (16 F to 57 F), and again under standard laboratory conditions. Each sequence included the 1975 Federal Test Procedure (exhaust emissions only), the Highway Fuel Economy Test and three short cycle tests. The vehicles were randomly obtained, tested in a 'as-received' condition, and work was performed between January and March 1978. Results show that HC and CO are most sensitive to cold temperature, while NOX is affected only slightly. Fuel economy suffered by an average of 7%, Vehicle fleets from manufacturers which used different control technologies were found to behave considerably differently at low temperatures.