The human gene coding for RBP4 has been assigned to 10q23----24 using a panel of somatic cell hybrids and in situ hybridization experiments. The mapping of the human RBP1, previously assigned by our group to chromosome 3 using a panel of somatic cell hybrids, was restricted to the region 3q21----22 using in situ experiments and Southern blots of genomic DNA from a hybrid retaining a portion of chromosome 3.