An alloplasmic line of maize (MDE) was produced by using the Multiple Dominant line (MDZ) as a recurrent male parent during 20 generations of backcrosses onto teosinte (Zea mays ssp. mexicana). The meiotic behaviour of both lines was carefully compared. The MDZ line has a transposon which can be activated by the cytoplasm of teosinte (Mazoti 1978). The analyses showed that all the individuals of MDZ had a regular meiosis, whereas the individuals of alloplasmic line presented several meiotic abnormalities in different parts of the panicle; the flowers showing cytomixis, fusion of nuclei, pseudomultivalents, asinapsis or persistent nucleolus at metaphase. The abnormal meiotic behaviour in alloplasmic line could be attributed to the action of the transposon carried by the MDZ line, which becomes activated in the cytoplasm of teosinte, such as it has been found by Mazoti (l.c.) for several morphological and cytological characteristics.