The influence of juvenile hormone (JH)-active chemicals on the settlement and metamorphosis of metatrochophore larvae of the polychaete annelidCapitellasp. I of theCapitellacomplex has been investigated. These studies demonstrate that JH-active chemicals are able to induce settlement and metamorphosis ofCapitellalarvae, and that these effects may possibly be mediated by protein kinase C induction. Evidence for the presence of JH-active compounds in marine sediments is also presented, suggesting that these chemicals may serve a natural role as chemical cues for settlement and metamorphosis forCapitellalarvae in the marine environment.