A series of experiments was performed to clarify whether photorefractoriness in male tree sparrows is maintained by an androgen-dependent mechanism. Castration did not raise plasma LH in photorefractory males held under a daily photoperiod of 20 h light: 4 h darkness (20L: 4D). Castrated photorefractory males were implanted with the antiandrogen cyproterone or injected s.c. with the antiandrogen flutamide to determine whether androgens which may be resistant to castration inhibit LH secretion. Neither cyproterone nor flutamide raised plasma LH above values found in castrated control birds. Castrated photorefractory males were treated with testosterone to determine whether plasma LH in photorefractory males is androgen-suppressible. Concentrations of plasma LH were independent of plasma testosterone over a wide range of concentrations. The lack of LH response to castration, to castration coupled with antiandrogen therapy, and to castration coupled with testosterone replacement argues that photorefractoriness in male tree sparrows is maintained by an androgen-independent mechanism.