INTRODUCTION The reduction of evaporative emissions from automotive carburetor bowls and fuel tanks is an important step in controlling air pollution. One possibility for limiting such losses is lowering of fuel front-end volatility. This would be expected to be detrimental to vehicle cold weather performance in the areas of starting and warm-up. Consequently@ this program was carried out to assess (1) the effect of reducing front-end volatility on start-up and warm-up in current cars@ (2) the minimum volatility for satisfactory start-up and warm-up performance over a wide temperature range@ (3) the variation in start-up and warm-up performance for two groups of current cars@ one with and the other without emission control systems@ and (4) the volatility limits which are imposed by normally encountered weaknesses of spark plugs@ battery and other engine components.