To identify sequences necessary for lens-specific gene expression, lines of transgenic mice were generated which contain murine alpha A-crystallin promoter sequences [-111 to +46 (alpha 111), -88 to +46 (alpha 88), and -34 to +46 (alpha 34)] fused to the bacterial chloramphenicol acetyltransferase (CAT) gene and CAT expression was analyzed. Mice carrying the alpha 111-CAT or the alpha 88-CAT fusion transgene expressed CAT exclusively in lens, except for one line containing alpha 111-CAT, which expressed low levels of CAT in several nonlenticular tissues. Transcription from these promoters in lens initiated at the same site as the endogenous alpha A-crystallin promoter. In one line of mice alpha 88-CAT transgene became active in the lens during embryonic development at approximately the same time that the alpha A-crystallin gene normally begins to be expressed. In contrast, the alpha 34-CAT fusion transgene, containing the TATA box but no sequences further upstream, was inactive in transgenic mice. Our data suggest that 134 bp of sequence (-88 to +46) in the murine alpha A-crystallin gene is sufficient to provide lens specificity, although we cannot rule out the possibility that other sequences also contribute to promoter function.