The expression of transforming growth factor-@b1 (TGF-@b1), and transforming growth factor-@b receptor type II (T@bR-II), were evaluated in periovulatory marmoset ovaries. Histochemical methods were used, in particular double-labelling techniques, in order to correlate growth factor/receptor expression with proliferation (Ki 67), apoptosis (TUNEL method) and luteinization (3@b-hydroxysteroid dehydrogenase (3@b-HSD)). The latter was used as a luteinization marker. Periovulatory ovaries are especially suited for studying all aspects since they typically consist of small non-luteinized follicles, large luteinizing follicles and corpora lutea accessoria (Clas), which have developed from large luteinizing follicles. TGF-@b1 and T@bR-II expression was found in luteinizing theca cells of large periovulatory follicles and in all luteal cells of Clas. Non-luteinized theca cells, including those of small follicles were always devoid of any immunostaining. Granulosa cells of small follicles were immunopositive for T@bR-II. Large follicles with granulosa cell immunoreactivity of both antibodies coexisted with non-reactive follicles of comparable size. The highest activity of the luteal marker enzyme 3@b-HSD was co-localized in the same cells that expressed TGF-@b1 and T@bR-II. The double-labelling experiments revealed that TGF-@b1 and T@bR-II expression is not correlated with proliferation or apoptosis of follicular cells. Our results indicate that TGF-@b1 and T@bR-II participate in differentiation processes, i.e. luteinization, rather than proliferation. In particular, the dynamics of T@bR-II expression appear highly related to the process of luteinization.