alpha B-Crystallin, first identified as a structural component of the vertebrate eye lens, is expressed at high levels in lens and at lower levels in a number of other tissues, most notably cardiac and skeletal muscle, kidney, and brain. We have cloned and sequenced the human alpha B-crystallin gene and show that it is structurally similar to its hamster homolog. We have also identified its transcription initiation site in human lens RNA. Functional analysis of a promoter fragment extending from -537 to +21 (relative to the transcription initiation site) and fused to the bacterial chloramphenicol acetyltransferase gene suggests that this fragment contains regulatory elements that function preferentially, but not exclusively, in lens. In contrast, this fragment is apparently insufficient to promote transcription in glial cells, as this construct functioned poorly in a glioblastoma-astrocytoma cell line (U-373MG) that synthesizes high levels of the endogenous alpha B-crystallin gene product.