Fumigation of eggs with the antiallatotropin precocene 2(P2) disrupted development late in embryogenesis in the American dog tick Dermacentor variabilis. An age (time) gradient of responses in embryos was noted. Subsequent developmental effects included partial failure of stadia to attach, feed, ecdyse and partial-to-complete sterility in adult females. No precocious metamorphosis or adultiformes were observed, but a change in sex ratio of surviving adults was noted. A subsequent application of juvenile hormone 3 (JH 3) to P2-sterilized females enabled them to feed and successfully complete the gonadotrophic cycle. Restoration of gonadotrophic function by exogenous JH 3 suggested the possibility of a naturally occurring JH in D. variabilis.