The influence of calcium and ABA on ethylene biosynthesis was investigated at different stages and patterns of tomato (Lycopersicon esculentum cv. Lichun) fruit to analyse the relationship between calcium and ABA in relation to the ethylene biosynthesis system. The ethylene production of discs excised from mature green tomato fruits increased rapidly with 100 μmol/l ABA or 100 mmol/l calcium treatment. The increase with the two treatments combined was more than that after application of a single chemical, which suggests that these two chemicals could play synergistic roles in the ethylene synthesis of mature green tomato fruits. It was also found that application of the calcium chelator EGTA inhibited ethylene synthesis, and the production of ethylene after application of EGTA plus ABA was higher than that after treatment with EGTA alone. However, the effect changed when immature fruits were treated with these chemicals. ABA inhibited ethylene synthesis obviously and calcium still promoted it. When we treated immature fruit discs with both calcium and ABA simultaneously, ethylene production was more than that of ABA and less than that of calcium, which indicates that ABA and calcium play agonistic roles in ethylene biosynthesis of the immature tomato fruit discs. Furthermore, ethylene release from transgenic antisense ACS immature tomato fruit discs with application of both calcium and ABA was inhibited markedly, but was stimulated when the mature fruits were treated with ABA and calcium. All of these data suggest that there are different relationships between calcium and ABA in the ethylene synthesis system in different patterns and stages of tomato fruit ripening.