Efficient plant regeneration and transformation procedures and the stability of the transgene are important to the success of the cotton and soybean biotechnology industry. Engineering herbicide resistance into plants will provide the potential solution to effective weed control in agriculture and reduce loss in crop yields due to weeds. It will also provide cheaper control and decrease environmental hazards. The aims of this study were to develop efficient regeneration and transformation protocols for commercially grown soybean and cotton in South Africa and to use tobacco as a model plant to study the stability of the pat gene through seed generations, successive generations and high temperature and drought stress regimes. Tobacco (Nicotiana tabacum cv. Samsun) leaf disks were successfully transformed with the pat gene. PCR analysis confirmed the integration of the pat gene in all nine transgenic plants and T1, T2 and T3 progeny. Successive generations, high temperatures and drought stress had no adverse effect on the stability and expression of the pat gene in the transgenic tobacco plants. In view of the economic importance of soybean (Glycine max) and cotton (Gossypium hirsutum) in South Africa and the potential to improve commerciallygrown cultivars by genetic transformation, a regeneration and transformation protocol using the shoot apical meristem and Agrobacterium-mediated DNA transfer was successfully developed, to obtain herbicide (Basta) resistant commercially-grown South African soybean and cotton plants for the first time. The frequencies of regenerated plants per meristem were 66% for Talana, 52% for Ibis, 90% for Sabie, 74.6% for LRCC 101, 69.5% for Palala and 70% for 107/1. Prior to transformation experiments, Talana and Ibis were screened for susceptibility to virulent Agrobacterium tumefaciens sis 43. Both cultivars produced tumours in response to infection and were therefore compatible hosts for Agrobacterium-mediated DNA transfer. Transformation of Talana, Sabie and 107/1 with the pat gene, was successfully achieved following wounding of the shoot apical meristem and injecting with Agrobacterium in the presence of acetosyringone. Transformed explants and shoots grew in the presence of kanamycin and PPT, indicating that the integrated pat gene was producing the enzyme PAT which was successfully detoxifying the herbicide PPT. Final transformation frequencies from the initial transformed meristems to regenerated plants were 1.06% for Talana, 2.3-3% for Sabie and 1.2-2.3% for 107/1. These transformation frequencies were higher than those reported in the literature. PCR analysis of the extracted DNA from transgenic soybean and cotton shoots confirmed the presence of the 558 bp pat coding region in the transformed plants. The success of this study on the regeneration and transformation of soybean and cotton indicates that South African agriculture now has available techniques for plant regeneration and recombinant DNA technology for crop improvement of soybean and cotton.