Abstract The breeding barriers between commercial litchi (Litchi chinensis Sonn.) and longan (Dimocarpus longan Lour.) cultivars were investigated by conducting reciprocal pollinations. This work has shown that it is possible to generate intergeneric hybrids using litchi as the female parent. Investigation of comparative in vivo pollen tube growth demonstrated that there is discrimination against cross- compared to self-pollen at all sites in the pistil. Pollen tubes were frequently observed in the ovary after cross-pollination in litchi but rarely in longan. Fruit production was reduced after crossing in both longan and litchi. Isozyme analysis using phosphoglucose isomerase revealed that hybrid progeny only developed when litchi was the maternal parent. Morphologically the hybrid plants were similar to the maternal parent but leaves were smaller. Three types of seeds developed in litchi following pollination with longan pollen. These were (1) normal seeds with a developed testa and embryo, (2) seeds with aborted embryos but normal testa development, and (3) seedless fruit where the ovule remained the same size as at anthesis without further development of embryo or testa. The potential germplasm available to improve these crops within the Sapindaceae is discussed.