Self- and cross-incompatibility of the olive cultivars Frantoio, Manzanillo, Kalamata, Pendolino, and Picual were investigated using a 5.3.5 diallel matrix. Pistils were collected seven days after controlled pollinations on the day of flower opening, and pollen tubes were detected by fluorescence microscopy. Diallel analysis showed significant specific combining ability, general combining ability and reciprocal effects between cultivars for pollen tube growth in the pistil. 'Frantoio' was cross-compatible, as either a male or female parent, with each of the other cultivars, butshowed a high degree of self-incompatibility.'Manzanillo', 'Kalamata', 'Pendolino', and 'Picual' were cross-incompatible, and all except for 'Manzanillo', were self-incompatible. It is concluded that 'Frantoio' is a good generalpolleniser for the other cultivars investigated. Pollen tube growth decreased in discrete steps from stigma to upper style, and from upper style to lower style, with the result that only one, and rarely more, pollen tube penetrated ovules. The sex ratio of flowers, and pollen viability using fluroesce in diacetate staining and in vitro germination, were examined. 'Frantoio', 'Manzanillo' and 'Pendolino' had more than 80% perfect flowers, while 'Kalamata' and 'Picual'had less than 30%. 'Frantoio' had the highest pollen viability, 'Kalamata' and 'Picual' were intermediate, and'Manzanillo' and 'Pendolino' the lowest. Pollen staining and both in vitro and in vivo germination provided the same male fertility rankings of cultivars.