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This paper describes aldehyde and unburned fuel emissions (UBF) measurements made on several light-duty, methanol-fueled vehicles with developmental 2.5-L engines and production and three-way catalytic converters. Emissions data were obtained under both steady-state and Federal Test Procedure (FTP) driving-cycle conditions. The data were then compared to those from a similarly equipped production gasoline vehicle. Before- and after-catalyst aldehyde and UBF emissions data are presented for three vehicle types as a function of equivalence ratio. In addition, aldehyde emission data for one of the methanol vehicles using a base-metal catalyst are discussed. The steady-state tests showed that both before- and after-catalyst aldehyde and UBF emissions are minimized by vehicle operation at lean equivalence ratios. The data also showed that formaldehyde accounted for 98% of the total aldehydes from the methanol vehicles, and only 31-54% of the total aldehydes from the gasoline vehicle.