A recent study using comparative mapping analysis suggests that the proximal segment of mouse chromosome 19 contains the mouse homologs of the human multiple endocrine neoplasia type 1 (MENl) flanking markers proximal to the locus. We have recently shown that phospholipase C-β3 (PLCB3) is a candidate gene for the MENl syndrome. In the present investigation we used fluorescence in situ hybridization with a genomic DNA clone for mouse Plcb3, and mapped the locus to chromosome region 19B. This is in agreement with the comparative mapping of the MENl flanking markers in mouse