To investigate developmental expression of the rat tyrosine aminotransferase (TAT) gene in normal and in albino lethal mice we generated transgenic mice carrying a fusion gene of TAT 5'-sequences (11 kb) and the bacterial chloramphenicol acetyltransferase (CAT) gene. In four lines, CAT activity was found only in liver. RNA analyses on a high-expressing line showed that transgenic expression follows expression of mouse TAT mRNA: it is inducible by glucocorticoids and activated perinatally. This perinatal activation of transgene expression does not occur in lethal albino mice (c14CoS/c14CoS) which are characterized by reduced mRNA levels of several liver-specific enzymes involved in gluconeogenesis. In conclusion, the data show that the 5'-flanking region of the rat TAT gene contains elements specifying regulated expression and establish that the 5'-flanking region of the TAT gene is responsive to the enzyme deficiency characteristic of the albino lethal mice.