The test procedures used to investigate the transient warm-up of two Ford 40 kW SI engines are described. Water, engine casing and lubricating oil temperatures were monitored and the rates of temperature rise determined as a function of engine speed and power. The temperature results showed that for both engines the lubricating oil was the slowest component in the warm-up and may be the limiting factor in engine warm-up. A particular emphasis has been placed on monitoring the gas composition during the warm-up. A special feature of this system is the use of two UHC FID analysers operating at 180°C and 2°C. The difference in the two UHC readings is a measure of the high molecular weight condensible UHC or unburnt liquid fuel that is emitted. It is shown that this is quite significant during the initial period of warm-up. NOx emissions showed a strong increase during the warm-up and this indicated that the combustion process took an appreciable time to achieve its maximum flame temperature.