During rodent mammary gland involution there is a dramatic increase in the expression of the transforming growth factor-β isoform, TGF-β3. The TGF-βs are multifunctional cytokines which play important roles in wound healing and in carcinogenesis. The responses that are activated in the remodeling of the gland during involution have many similarities with the wound healing process and have been postulated to generate a mammary stroma that provides a microenvironment favoring tumor progression. In this review we will discuss the putative role of TGF-β during involution, as well as its effects on the mammary microenvironment and possible implications for pregnancy-associated tumorigenesis.