The effect of kallikrein on the Sertoli cells was investigated to determine the rat testicular androgen binding component (ABC = androgen binding protein + androgen receptor) concentration using the dextran-coated charcoal method. The results showed that the concentrations of testicular ABC were increased significantly by the administration of kallikrein to levels approaching those seen after stimulation by LH-RH or FSH. Therefore, it is suggested that kallikrein has an effect that influences the Sertoli cells directly or indirectly.