We have previously demonstrated that one member of the alpha-tubulin multigene family, termed T alpha 1 in rats, is a panneuronal gene that is regulated as a function of neuronal growth and regeneration. Moreover, 1.1 kb of the 5' upstream region from this gene is sufficient to direct expression of a marker gene to growing neurons in transgenic mice. In this report, we have characterized the distribution of the T alpha 1:nlacZ transgene in the mature central nervous system in two lines of transgenic mice and have compared its expression to that of the endogenous T alpha 1 alpha-tubulin mRNA. These results demonstrate that the pattern of expression of the T alpha 1:nlacZ transgene is similar to that of T alpha 1 mRNA, with a few notable differences. Furthermore, expression of the transgene and the mRNA within the mature brain is panneuronal and, in many cases, is highest in those populations of neurons that show some capacity for morphological growth. These results, together with our previous studies on mature regenerating neurons (Gloster et al. [1994] J. Neurosci. 14:7319-7330; Wu et al. [1994] Soc. Neurosci. Abstr. 20:542) suggest that the T alpha 1:nlacZ transgene will provide a useful marker of growth-associated gene expression in the mature nervous system.