F 1 hybrids were obtained between two co¤ee species with the same chromosome number (2n"22) but with di¤erent nuclear DNA contents [C. pseudozanguebariae (PSE) 2C"1.13 pg and C. liberica var ÔdewevreiÕ (DEW) 2C"1.42 pg]. G2 hybrids were obtained by open-pollination of the F 1 hybrids. Genomic in situ hybridisation (GISH) and ßow cytometry were used on six F 1 hybrids and seven G2 hybrids to determine their parental chromosomic contribution and their nuclear DNA content (qDNA), respectively. GISH e¦ciently identiÞed chromosomes from both species. F 1 hybrids had a qDNA intermediate between that of the parental species and contained the expected 11 chromosomes from each species. There was a linear relationship between the number of PSE chromosomes and the nuclear DNA content, which indicates that ßow cytometry can be used to give a rough estimate of the parental chromosomic contribution in G2 hybrids.