A histochemical avidin-biotin technique with three different alpha 1-acid glycoprotein glycoforms showed pronounced alterations in the cellular localization of two alpha 1-acid glycoprotein lectin-like receptors during cell differentiation in the developing rat testis. The binding of alpha 1-acid glycoprotein glycoforms to their receptors is inhibited by steroids. Testosterone, oestradiol and progesterone inhibited the binding of alpha 1-acid glycoprotein glycoform A to its receptor. Cortisone, aldosterone, oestradiol and progesterone inhibited the binding of alpha 1-acid glycoprotein glycoforms B and C to their receptor. A difference in the cellular content of alpha 1-acid glycoprotein glycoforms and alpha 1-acid glycoprotein receptors separates the spermatocytes and the early spermatids from the late spermatids. The difference in receptor composition implies a difference in the effect of different steroid hormones. The Leydig cells contained alpha 1-acid glycoprotein and lectin-like receptors for one of the glycoforms of alpha 1-acid glycoprotein from birth. The interaction between alpha 1-acid glycoprotein glycoforms and their receptors may modulate the actions of testosterone and other steroids in the testis.