Hb Lepore-Hollandia, identified in a Thai patient, was found to be due to a new cross-over between IVS1-nt 42 and nt 56 of the delta- and beta-globin genes. This differs from a previous case which crossed-over between codon 22 and IVS1-nt 16. Two independent homologous unequal cross-over events account for these two Lepore-Hollandia genes.