Recent studies indicated that c-Fos protein may be mediating stress-elicited transcriptional activation of genes involved in neurotransmitter biosynthesis. However, direct evidence for c-Fos mediating these changes in gene expression has been lacking. Mice with disrupted c-fos gene (+/- or -/- genotypes) were used to examine the effect of immobilization stress on a group of stress-responsive genes. In male adrenals, c-Fos was found not essential for stress-elicited activation of expression of tyrosine hydroxylase, dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase, or neuropeptide Y. In females, immobilization failed to induce adrenal DBH in the c-Fos-deficient mice. In brainstem, c-Fos was indispensable for elevation of DBH mRNA in both genders. The gene, gender, and tissue specificity in the requirement for c-Fos points to diversity in adaptation mechanisms to stress.