We tested the ability of several GnRH analogues to suppress pituitary-testicular activity and potentially musth in free-ranging African elephants (Loxodonta africana). In Study 1, adult bulls were given 4 or 12 mg GnRH antagonist (Detirelix) or saline i.m. on day 0 (n = 3 bulls per treatment). Animals were then recaptured on day 2 (about 48 h later) and given 300 micrograms GnRH i.v. to assess the ability of the antagonist to block pituitary activity. Detirelix reduced (P < 0.05) basal concentrations of serum LH and testosterone on day 2 compared with day 0, with no effect of dose. Similarly, LH and testosterone release induced by GnRH were also reduced (P < 0.05) in the Detirelix-treated bulls (50-70% reduction in peak concentrations). In Study 2, elephants were given 30 mg of a structurally similar GnRH antagonist (103-201-40; n = 6), 22.5 mg of a long-acting GnRH agonist (Lupron Depot; n = 4) or D-mannitol carrier (n = 4) i.m. on day 0. All bulls were recaptured and given GnRH on day 2 (103-201-40 treatment) or on days 2 and 20 (Lupron Depot treatment) after the initial injection. In contrast to Detirelix, 103-201-40 did not inhibit basal or GnRH-induced LH or testosterone secretion. Pituitary-testicular responses to Lupron Depot were initially stimulatory, as evidenced by increased (P < 0.05) LH and testosterone secretion on days 0 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)