PCT No. PCT/EP93/00463 Sec. 371 Date Jan. 20, 1995 Sec. 102(e) Date Jan. 20, 1995 PCT Filed Feb. 25, 1993 PCT Pub. No. WO93/17116 PCT Pub. Date Sep. 2, 1993The invention provides Agrobacterium strains capable of producing a cite-specific recombinase capable of effecting site-specific recombination of a first and a second recombination site in Agrobacterium strains, when present therein, comprising a structural DNA sequence encoding said recombinase and a DNA sequence capable of controlling expression in Agrobacterium strains. The invention also provides methods for using the strains to transform plant cells.