Total immunoglobulin G (IgG) in rat testicular interstitial fluid and serum was measured by two-site enzyme-linked immunosorbent assay, which displayed minimal cross-reactivity with IgA or IgM. Normal adult testicular fluid IgG concentrations (2.67 +/- 0.98 mg/ml) were found to be 65% of the levels found in serum. Disruption of seminiferous tubule function by experimental cryptorchidism had no effect on either testicular or serum IgG concentrations. Castration also had no effect on serum IgG concentrations. The effect of the Leydig cell cytotoxin, ethane dimethane sulfonate, on IgG concentrations was obscured by the observation that dimethyl sulfoxide (the carrier solvent) itself effectively eliminated the IgG concentration gradient across the testicular microvasculature. In normal and cryptorchid rats, serum IgG and thymus weights showed no correlation with serum inhibin concentrations measured by radioimmunoassay, although thymus weights were significantly increased in castrate rats. The data confirm that the permeability of the rat testis to circulating IgG is relatively high compared with other tissues and suggest that the testicular transendothelial transfer of IgG is unaffected by changes in testicular activity or hormone secretion. The high intratesticular concentration of IgG and its apparent lack of local regulation provide further evidence that the phenomenon of immune privilege in this tissue cannot be attributed simply to restriction of immune effectors from the testicular environment. The data also indicate that serum IgG levels in the adult male rat are not influenced in the short-term by changes in peripheral testicular androgen levels.(ABSTRACT TRUNCATED AT 250 WORDS)