Abstract Tomato fruit was harvested at breaker stage and stored at 15°C. When ripening had developed to the pink stage, fruit was transferred at 6 h intervals, from 15 to 20, followed by 25 and 30°C, and then returned back to 20°C. As the temperature increased from 15 to 30°C, CO 2 production by the fruit significantly increased. Maximum C 2 H 4 production occurred when fruit was held at 20°C. As the temperature rose from 20 to 30°C, both C 2 H 4 production and the ACC level declined. The effect of temperature on C 2 H 4 production is reversible since the same levels of C 2 H 4 were produced by fruit held at 20°C whether they were previously held at 15 or 30°C. When fruit was held at 35°C, the ACC level sharply increased while C 2 H 4 production continue to decrease. In excised pericarp disks, ACC conversion to C 2 H 4 increased as the temperature increased, reached its maximum rate at 30°C, but was inhibited at 35°C. The inhibition of C 2 H 4 biosynthesis at temperatures between 20 and 30°C is attributed only to the reduction in ACC synthesis. At 35°C however, both ACC synthesis and its conversion to C 2 H 4 were inhibited, but the inhibition was sudden and more pronounced on ACC conversion to C 2 H 4 .