This experiment was done to clarify the influence of the absence of the genes responsible for ripening and ethylene production using three types of tomato fruits; cv. Rutgers as ripening type, nor mutant as slight ripening type and rin mutant as non-ripening type. Changes in 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity and ethylene forming enzyme (EFE) activity in these tomatoes were measured at several stages. ′Rutgers′ tomato produced ethylene in ripening stage, whereas nor tomato produced ethylene slightly and rin hardly produced it except for production due to decay of fruits. It seems that ethylene production of ′Rutgers′ is attributed to accumulation of ACC and increase in EFE activity during climacteric, and insufficient ethylene production of nor tomato fruit is due to accumulation of ACC only, without increased EFE activity in the tissue. And very little ethylene production of rin is due to the small amount of ACC content without increased EFE activity.