Mollusks from the volcanic islands of Oahu, Hawaii; Tahiti, Society Islands; and Rarotonga, Cook Islands; and from the coral atoll of Majuro, Marshall Islands, were studied in an attempt to determine which species might serve as intermediate hosts of the rat lung worm, Angiostrongylus cantonensis. Mollusks found infected with A. cantonensis on the volcanic islands were all common, introduced species that have been referred to as “tropical tramps.” They included the veronicellid slugs, Laevicaulus alte (only on Oahu) and Vaginulus plebeius (only on Rarotonga and Tahiti); the subulinid snails, Subulina octona and Prosopeas javanicum; the helicid snail, Bradybaena similaris; and the limacid slug Deroceras laeve. A. cantonensis was also found in the giant African snail, Achatina fulica, which is common on Oahu, but not present on Rarotonga or Tahiti. A large proportion of the veronicellid slugs and A. fulica contained A. cantonensis larvae, often more than 1,000 per infected mollusk. The other mollusks were much less commonly and less heavily infected. Although no marked seasonal fluctuations in the prevalence of infection was noted, a smaller percentage of mollusks was found infected, and mollusks generally contained smaller numbers of larvae, in drier areas. At least five species of aquatic and amphibious snails, of five families, were examined from the island of Oahu, but only one species, the pilid snail, Pomacea paludosa, was found infected with A. cantonensis. Ten species of snail, of six families, were examined from Majuro, but none was infected.