SUMMARY: Mutants of ground nut (Rhizobium cowpea group) strain gr3 were isolated using ultraviolet radiation and N-methyl-N'-nitrosoguanidine (NTG) as mutagenic agents. An adenine-requiring mutant was used as the recipient and its wild type as the donor in transformation studies. Initially minimal medium supplemented with 2 μg. adenine/ml. was used for the development of competence. The maximum transformation frequency was obtained after about 120 min. incubation. Supplementation of minimal medium with yeast extract and vitamin-free Casamino acids without the addition of adenine stimulated competence to a large extent. The competence was not further stimulated by any of the divalent ions used. The optimum DNA concentration for maximum transformation frequency was about 50 μg./ml.