Direct gene transfer into plant protoplasts has been recently developed, and conditions for high frequency transformation of SR1 tobacco protoplasts established. In this paper we analyse numerous transformation parameters in a comparative study on SR1 Nicotiana tabacum and N. plumbaginifolia, and report on a simple chemical technique for very efficient protoplast transformation. It is based on the synergistic interaction of MgCl2 and PEG. The technique yielded up to 1400 transformants per 3×10(5) treated N. tabacum protoplasts (up to 4.8% of the survivors, late selected clones). Using N. plumbaginifolia, the frequencies were 10-fold lower, indicating that the 'competence' for transformation has a species-specific component.