A heterozygous translocation involving two non homologous chromosomes was observed in a hybrid between Zea mays L. and Z. mexicana (Schrad.) Kuntze. The cytological observations were made at the microspore phase. A cross-shaped synaptic figure formed by the translocated chromosomes was shown at pachytene as well as the chain configurations at diakinesis and ring shaped formations at metaphase I. Pollen sterility was 44.0% .+-. 1.2 and it was probably due to the presence of the translocation rather than to the interspecific hybridization itself. Because of poor pachytene spreading, chromosomes involved in the translocation could not be identified. However, they appear to belong to the group of the large chromosomes (1, 2 or 3).