α<sub>2</sub>-Macroglobulin (α<sub>2</sub>M) is a large plasma glycoprotein that has long been known as an irreversible inhibitor of a variety of proteinases. More recently, it has been reported that numerous growth factors, cytokines and hormones bind to α<sub>2</sub>M through diverse mechanisms. We review here a series of observations from our laboratory that support the concept that α<sub>2</sub>M is a carrier protein for transforming growth factor-β (TGF-β) and allows this factor to act as an autocrine regulator of adrenocortical steroidogenic functions. α<sub>2</sub>M was found to be synthesized and secreted by primary cultures of bovine adrenocortical cells in fairly large amounts (1 μg/l0<sup>6</sup> cells/24 h). TGF-β is also secreted by this cell type, although under a latent form. Two distinct latent TGF-β complexes have been characterized in adrenocortical cell conditioned medium, one of which is a complex between α<sub>2</sub>M and TGF-β. Although α<sub>2</sub>M prevents the binding of TGF-β to its membrane receptors, long-term incubation of α<sub>2</sub>M with adrenocortical cells results in inhibition of cortisol production similar to that observed in the presence of TGF-β alone. Taken together, these observations suggest that adrenocortical cells can release active TGF-β from its latent complex with α<sub>2</sub>M through an unknown mechanism. α<sub>2</sub>M can therefore be considered as a TGF-β carrier protein.