Adult female green iguanas (I. iguana) were treated with repetitive pulses of chicken gonadotropin (d-Arg6 chicken II) releasing hormone (GnRH) delivered by i.p. osmotic pumps. Total estrogen levels in serum decreased from 37.3 .+-. 18.0 pg/ml to 5.4 .+-. 4.6 pg/ml 9 days after the pump was implanted. Estrogen levels returned to pre-implant levels 5 days after the end of the treatment period. The behavior of male iguanas, housed with the treated females, was influenced while the pumps were functioning. The frequency of assertive displays between males increased 3-fold after 7 days of GnRH treatment. Males actively interposed themselves between their female and other males during the same period.