This study was designed to determine how to suppress behavioral effects of androgens with a pure non-steroidal antiandrogen, Hydroxyflutamide (OHF). The major dependent variable was yawning behavior of castrated adult male rhesus macaques. Injections of testosterone propionate (TP) increased yawning frequency and cessation of TP injections produced a decrease in yawning frequency. A similar decrease was observed with simultaneous injections of TP and OHF. It has been found that the dose of OHF injected subcutaneously should be 80 times that of TP to block the effects of either physiological or supraphysiological doses of TP. (C) 1994 Academic Press, Inc.