Introduction: It is known that fertility of normal high altitude dwellers is similar to that at sea level. Objectives: To determine the hypophyso- gonadal reserve using a pulsatile methodology with low doses of GnRH. Design: Experimental, basic study. Setting: Instituto de Investigaciones Clinicas, Universidad Nacional Mayor de San Marcos, Lima, and Laboratorio de Ciencias Biologicas, Universidad San Antonio Abad, Cusco, Peru. Participants: Sea level and high altitude normal subjects. Interventions: Twelve normal male high altitude dwellers (Cusco, 3395 m.a.s.l.) and 12 subjects living at sea level (Lima, 150 m.a.s.l.) were submitted to an intermittent intravenous infusion of GnRH for 24 hours. Serum LH, FSH and testosterone concentrations were measured using RIA techniques. Main outcome measures: LH, FSH y testosterone concentrations. Results: LH, FSH and testosterone basal concentratio...