Ovarian dlevelopmnent, vitellogenesis, andt etnbrvogenesis in recently matedlce fiemnales of tlhe sofi tick Ornithodoros parkeri Coolev were prevented by topical application of the insect antiallatotropin precocene 2. ThCe blockage was relieved by topical application of jtivenile hormonoe. Cancellation of the anti-juvenile hormnone jJects of precocene 2 and the reestablishment of oogenesis (and oviposition in one specimen) bv a naturally occurring insect juvenile hormone argues strongly for a physiological role of juvenile hormone in acarine reproduction.