The C-reactive protein is the major acute phase protein (APP) in humans which binds lectin-like to different membraneous structures and exerts an important function in non-specific defense. Because of a pentameric molecular symmetry CRP as well as serum amyloid P component (SAP) and hamster female protein (FP) was merged into a special protein family named pentraxins. In rats a protein was found referred to as rat FP which was close related to hamster FP with respect to hormonal regulation and APP nature as well. Based on this conformity the molecular structure of rat FP was analyzed and as the results a pentameric structure could be demonstrated for rat FP, too. Furthermore, the response of rat CRP and FP on injection of adrenal hormones, agents being involved in acute phase reaction, was investigated. Epinephrine administration led to an increase in CRP and a decrease in FP serum concentration. Dexamethasone has the same effect in case of FP and changed the CRP concentration in a biphasic way with a maximum at about 0.01 mg/kg, a minimum at 0.6 mg/kg and a return to control values at 1.8 mg/kg. Thus, the results indicate a neuroendocrine control of CRP and FP but probably in a different way. Using FITC-labelled lectin the exposition of galactose-containing membraneous structures could be demonstrated in carbon tetrachloride-injured liver tissue in contrast to controls. These binding sites are in accordance with increased FP-binding shown by immunofluorescence histochemistry. Thus, lectin-like properties may be ascribed to rat FP comparable to CRP and SAP activity. The results are discussed with respect to findings from literature that also the acetylcholine receptor seems to have a pentameric structure.