The conjugal transfer of recombinant plasmids into a gellan gum-producing, rifampicin-resistant strain of Pseudomonas elodea and into one of its non-producing variants, was studied in order to facilitate the cloning of gellan genes. The mobilization frequency of recombinant plasmids derived from pKT240, and of cosmid pJRD215 from Escherichia coli HB101 (hsdM), into the mucoid strain was below the values for the non-mucoid variant and decreased exponentially with plasmid size. Reducing the mating time on solid surfaces led to higher mobilization frequencies. Under optimal conditions, a gene bank (40-50 kb) constructed in the cosmid pJRD215 was efficiently mobilized into Gel- mutants during complementation experiments.