Protoplasts of Nicotiana debneyi were inactivated by X-ray irradiation (10 KR) and were fused with a recessive chlorophyll mutant (consolation 402) tobacco (N. tabacum) protoplasts. Under no selection pressure on the PEG-treated protoplasts, two types of regenerates appeared; one was a normal consolation 402, and the other male sterile consolation 402. Between these two types, no morphological and cytological differences exist except flower morphology. Male sterile regenerates exhibited a distinct flower type which was identical to that of tobacco with N. debneyi's cytoplasm produced by sexual crosses. Although no experiments have been performed asking mitochondrial constitution of these male sterile plants, t is likely that N. debneyi's cytoplasmic factors have been transmitted to the male sterile plants.