Anestrous ewes (3) were treated with a 500 ng GnRH [gonadotropin releasing hormone] pulse administered via a jugular cannula every 2 h for 40-80 days. Plasma concentrations and therefore presumed ovarian activity changed cyclically with each progestational cycle (10) lasting 14.0-18.5 days. By increasing the frequency of GnRH secretory episodes from an apparent endogenous level of 1 episode per 3.6 h to at least 1 every 2.0 h, cyclic ovarian activity can be restored to seasonally anestrous sheep.