Expression of nicein is specifically hampered in the severe form of junctional epidermolysis bullosa (JEB), a recessive genodermatosis characterized by blister formation of integument believed to be due to defects in hemidesmosomes. Nicein genes are therefore the prime candidates for involvement in JEB. To map the gene encoding the 125-kDa subunit of nicein, the authors used the cDNA Kal5.5C coding for the amino-terminal domain of the protein. In situ hybridization was carried out on chromosomes in phytohemagglutinin-stimulated blood lymphocytes of healthy donors. In 100 metaphases examined, 153 silver grains were found associated with chromosomes; 45 (29%) of these were located on chromosome 1, and 33 (73%) of these 45 grains mapped to region 1q32.1-q41 with a maximum in band 1q32. To confirm the regional localization of the genes for nicein subunits of 100 and 125 kDa, fluorescence in situ hybridization was performed on normal lymphocytes from two unrelated normal males and fibroblast cell lines GM00257 (karyotype 46,XX, t(1;2)(1q32;2p23)) and GM004088 (46,XY,t(1;4)(q32;p16)). It was thus confirmed that the genes for nicein 125- and 100-kDa subunits are localized at 1q32 and 1q25-q31, respectively. 9 refs., 1 fig.