Alloplasmic plants of rye, Secale cereale L., with cytoplasm of Triticum durum Desf. are studied in order to investigate the causes of male sterility. Meiosis can be considered as normal because the alterations found had little entity. Abortion of pollen was progressive during microspore maturation; however, the variation among plants in percentage of aborted pollen was high (from 10%. to 98%.), being the average 29.3%. Histological observations showed that the only alteration in anther wall tissues was the non total disappearance of tapetum. So, the fusion of neighbouring loculi and the subsequent dehiscence of the anther was impeded. Therefore, the male sterility in this alloplasmic rye is a case of functional male sterility because the pollen being partially fertile cannot intervene in fertilization by the indehiscence of the anthers. The independence between pollen abortion and tapetum perdurability is discussed. Other events as pistilloidy are described.All studies were made simultaneously with the normal rye counterpart as control.