Castrated male rats were subcutaneously injected testosterone (5 and 10 mg) or a mixture of beta-estradiol and progesterone (1 microg + 2 mg), to determine whether sex steroid hormones (testosterone, beta-estradiol, progesterone) might affect the content of sialoglycoproteins, the content and pattern of lipid-bound sialic acid, and the activities of sialyltransferase (SAT) I and SAT II in the Golgi-rich membrane fraction isolated from rat kidney. During four days testosterone did not affect significantly the content of proteins, sialoglycoproteins and total gangliosides, but increased the content of b-series gangliosides from 0.05 +/- 0.006 (untreated animals injected subcutaneously with 0.1 ml DMSO for four days) to 0.16 +/- 0.02 nmol sialic acid (SA) per mg protein (castrated animals injected subcutaneously with 10 mg testosterone/0.1 ml DMSO for four days). This increase was due to the increase in GD3 ganglioside from 0.03 to 0.12 nmol SA/mg protein, and to the decrease of GM3 ganglioside from 0.06 to 0.03 nmol SA/mg protein by testosterone administration. The major ganglioside in the rat kidney was GM3, constituting 63% (control group) and 51% (castrated animals injected daily with 10 mg testosterone) of all gangliosides. Castration itself induced an increase in the rat kidney SAT I and SAT II activities from 712 +/- 130 to 1723 +/- 412 pmol/h x mg protein and from 208 +/- 48 to 751 +/- 176 pmol/h x mg protein, respectively. However, subsequent administration of testosterone, at the highest concentration tested, reversed this effect. In the kidneys of castrated rats, a mixture of beta-estradiol and progesterone decreased SAT II activity from 208 +/- 48 to 87 +/- 33 pmol/h x mg protein.