High-voltage shock within a very short duration under the proper conditions causes cells to incorporate exogenous macromolecules. This technique, electroporation, has been widely used in recent years to transform many organisms. We determined optimum conditions for fission yeast transformation using this method. Of nineteen combinations of electric field strength and pulse time examined, 1.75 kV/0.2 cm, 4 msec pulse was found to provide approximately 4.0 x 10(5) transformants per micrograms of DNA. Other factors responsible for the transformation efficiency in fission yeast are also discussed.