Factors affecting the PEG-mediated transformation and electrotransformation of Streptomyces avermitilis protoplasts, an industrial avermectin high-producer, were evaluated. The maximum protoplast transformation efficiency under optimum conditions with PEG was 3 × 10 6 transformants per µg plasmid pIJ702 DNA. The efficiency of electrotransformation with the same plasmid the intact cells grown in medium with 0.5 mmol/L CaCl 2 , suspended in buffer with 0.5 mol/L sucrose +1 mmol/L MgCl 2 , and pulsed at an electric field strength of 10 kV/cm, 800 Θ, 25 µF, was of 2 × 10 3 transformants per µg DNA. When the cells were electroporated after mild lysozyme-treatment, the efficiency was up to 10 4 transformants per µg DNA. Electroporation of protoplasts and germlings had a lower efficiency (10 2 transformants per µg DNA). We report that electroporation under optimum conditions can be used for direct transfer of nonconjugative plasmid pIJ699 between two different Streptomyces species, S. avermitilis and S. lividans .