Three cetaceans trom Monterey Bay, California (USA), were infected with lung nematodes. A beaked whale calf, Mesoplodon sp. was infected with adult Halocercus sp. This represents a new host record for this nematode. The lungs of a northern right whale dolphin calf, Lissodelphis borealis, contained an unidentified nematode similar in size to Halocercus sp. The presence of Phyllobothrium delphinitype cestode larvae in its blubber is evidence that the calf was feeding on invertebrates. A pregnant harbor porpoise, Phocoena phocoena was infected with the lung nematode H. invaginatus, but the fetus was uninfected. We found no direct evidence of a transplacental mode of transmission for Halocercus sp.