Three cetaceans from 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 delphini-type 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.