Results from eight years of research on Coffea canephora, C. congensis and C. dewevrei are reported. Some observations have already been published. These three species are self-sterile, no fruit being formed after selfing. Nevertheless, embryo-sac development and microsporogenesis are normal and no other factor prevents pollination. The pollen grains vary greatly in size. Those of Coffea congensis from Uganda germinate abnormally, producing cytoplasmic expansions instead of pollen tubes. Kept under laboratory conditions, the pollen of the three species lost viability within seven days. Through intra-specific crosses several compatible clones have been established. The observations made indicate that in Coffea canephora, C. congensis, and C. dewevrei there is genetic self-incompatibility; in C. congensis there is in addition male sterility. In Coffea canephora, a species that was studied in more detail, it has been possible to determine the «S» factors for incompatibility controlling the relations between pollen tube and stigma. Some plants of this species could already be classified in three classes: S1S2, S1S3 and S2S3.