The 78,000-dalton glucose-regulated protein (GRP78) is a stress-inducible protein localized in the endoplasmic reticulum. It has been identified as the immunoglobulin heavy-chain-binding protein. We report here a high level of GRP78 expression in a B-cell myeloma line, NS-1, which produces only kappa light-chain proteins but is unable to secrete them. GRP78 transcription was enhanced in NS-1 cells, resulting in higher levels of GRP78 mRNA and protein than in non-immunoglobulin-producing cells. Furthermore, the nonsecreted light chains in NS-1 cells were found in specific association with GRP78. We hypothesize that in nonsecreting lymphoid cells, the presence of free, unassembled light chains in the endoplasmic reticulum could result in increased transcription of the GRP78 gene and that GRP78 can also bind to immunoglobulin light chains.