Summary. To explore the effectiveness of modified inversion-polymerase chain reaction (I-PCR) to detect the factor VIII (FVIII) intron 22 inversion (Inv22) for genetic diagnosis and prenatal diagnosis in haemophilia A (HA). Both modified I-PCR and LD-PCR were applied to analyse the FVIII Inv22 for 24 patients with HA. Prenatal diagnosis was performed on six foetuses. Foetal blood samplings were carried out by cordocentesis from 22 to 26 weeks of gestation. Ten patients with FVIII Inv22 in 10 HA families were found, and the remaining 14 patients were found without the Inv22 in 19 HA families. Prenatal diagnosis confirmed that four foetuses were normal and all of them born normally. However, two foetuses had been identified as abnormal and undergone abortion. Compared with LD-PCR, modified I-PCR is more rapid and convenient for detecting the FVIII Inv22 in genetic diagnosis. It is recommended that a patient undergoes both modified I-PCR (to detect the FVIII Inv22) and biochemical assay (to measure the FVIII activity of umbilical cord blood) in prenatal diagnosis. When we have more experience, the DNA samples from chorionic villus or amniotic fluid can be analysed for prenatal diagnosis using the modified I-PCR alone.