Effects of ecdysone, 20-hydroxyecdysone (20E), and an ecdysone agonist, halofenozide, were tested against the Formosan subterranean termite, Coptotermes formosanus Shiraki, and the eastern subterranean termite, Reticulitermes flavipes (Kollar), in a 12-d no choice assay. Approximately 22-26% of R. flavipes and C. formosanus exhibited symptoms of hyperecdysonism, that is, "jackknife" position, when exposed to ecdysone and 20E at 1,000 ppm, respectively. High mortalities were recorded for both termite species in ecdysone and 20E at 100 and 1,000 ppm, but only at 10,000 ppm for halofenizide. Termites are known to move back to the central nest before the onset of ecdysis, and those that ingested lethal doses of chitin synthesis inhibitors (CSIs) die near the royal pairs, which partially accounts for the success of CSI baits to eliminate subterranean termite colonies. Because ecdysteroids and their agonists induce molting in termites, incorporation of these compounds into baits could potentially achieve the same colony elimination. This study showed that lethal time (12 d) of ecdysteroids and ecdysone agonist is shorter than that of a CSI (45 d); hence, the baiting time should be reduced by more than a month when they are incorporated in termite baits.