Tomato plants were studied to see how they respond to different temperatures before and after flowering. When exposed to moderately high temperatures, plants grown at cooler temperatures had fewer fruits if stressed before flowering. But if stressed after flowering, fruit set was not affected. Plants grown at higher temperatures had no fruit set unless given a break before flowering. The most sensitive period for plants was 7-15 days before flowering. High temperatures affected pollen development, but this was reduced if plants had a break before flowering.