A monoclonal antibody (mAb), designated PS-7.6, was previously shown to enhance the growth-promoting activity of porcine growth hormone (pGH) in an experimental hypophysectomized (hypox) rat model. The long lasting effect of PS-7.6 was postulated to be a result of the induction of anti-idiotypic antibody (anti-id) in these treated animals. An attempt was made in this report to further explore this issue. It was demonstrated that mice following immunization with PS-7.6 were capable of producing anti-id in serum. The antibody titers of mice immunized with a mixture of PS-7.6 and pGH were much higher than that of those being immunized with PS-7.6 alone. A monoclonal anti-id, designated 2A6, was generated and found to recognize the intact PS-7.6 and its F(ab')2 fragment under non-reducing condition in Western analysis. However, it did not interact with reduced PS-7.6, suggesting the necessity of both H and L chains for the expression of a conformational idiotype. In radioimmunoassay, 2A6 competed with pGH for the binding to PS-7.6, but failed to do so with a control anti-pGH mAb recognizing a distinct pGH epitope from that of PS-7.6. Results from a biospecific interaction analysis which monitored the molecular interactions in a real-time fashion confirmed the facts that 2A6 specifically recognized the variable region of PS-7.6 and that the recognition was inhibited by the presence of pGH. Enzyme-linked immunosorbent assay provided further evidence to indicate that 2A6 bound to GH binding protein, i.e. the soluble GH receptor, and pGH prevented this interaction in a dose-dependent manner. The biological effect of 2A6 was evaluated in hypox rats and shown to promote the growth of these GH-deficient animals. Taken together, the present findings clearly demonstrate that 2A6 raised against a growth-enhancing anti-pGH mAb mimics pGH both conformationally and functionally.