Tomato plants that are delayed in fruit ripening have been developed by Agrobacterium tumefaciens-mediated transfer of a gene encoding 1-aminocyclopropane-1-carboxylate deaminase (ACCd) from the soil bacterium Pseudomonas chloroaphis into the tomato genome. Two delayed ripening (DR) tomato lines are characterized in this paper. Line 8338, transformed by a double border plasmid vector, contains a single copy of the accd gene, and DNA outside the plasmid border sequences was not transferred to the plant genome. Line 5673, transformed by a single border plasmid vector, contains a single copy of the accd gene plus tandem, incomplete copies of the gene. The mean expression levels of ACCd in fruit collected from four field trials were 39.4 and 20.6 mu g/g of fresh weight for lines 8338 and 5673, respectively. Fruit ethylene synthesis was significantly reduced, and time for fruit to ripen was extended for both DR lines compared to the parental line UC82B. Introduction of the accd gene and the delayed ripening trait into appropriate tomato varieties will potentially allow production of tomato fruit with superior flavour quality.