Clues for overcoming fetal ( y -) giobln gene repression in adult human erythroid cells may come from understanding why repression of isolated y-giobin genes has not previously been achieved In the adult erythroid environment of mouse erythroleukemia cells (MEL). Repression of human y-globln genes has been demonstrated in MEL cells when transferred as part of the entire p-globln gene cluster packaged in chromatin. Major differences in these approaches are prior packaging Into chromatin and the presence of additional sequences, notably from the locus control region (LCR). In this report we focus on the contribution to y-giobin gene repression that multiple elements of the LCR may have. We first show preferential activation of pglobln genes over y-globln genes in MEL cells when linked to each other and to LCR sequences containing the core elements of DNase I hypersensitive sites 4, 3, and 2. Removal of the HS4 element had no effect, however, removal of the 225 bp HS3 core element resulted in a five-fold Increase in yglobin gene expression. The enhancer 3' to the Ay-globln gene also had no apparent effect on y-giobln gene expression. These results provide first evidence of y-giobln gene repression Involving the core region of HS3 in the presence of the core region of HS2 and a pglobin gene. A mechanism for repression Involving sequestration of the y-promoter away from the strong enhancer activity of HS2 is proposed.