The external stimuli that trigger ovulation and oviposition in anuran amphibians are poorly understood. We determined experimentally when during the mating process female Barking Treefrogs (Hyla gratiosa) become irrevocably committed to oviposition. We captured females at different points during the mating process, held them overnight without mates, and determined the following morning whether females had oviposited. Females arriving at the chorus and captured before entering amplexus did not oviposit, whereas 22% of females captured immediately after entering amplexus did. Ninety percent of females allowed to remain in amplexus for 1 h oviposited, and all females allowed to remain in amplexus for 1.5 h oviposited. Females that remained in amplexus for 1 h released significantly fewer eggs than did females that remained in amplexus for 1.5 h. These results indicate that amplexus, or a cue correlated with amplexus, triggers oviposition and that the number of eggs ovipositied increases with time spent in amplexus.