Perkinsus olseni infections are reported at 10%-84% prevalences among Austrovenus stutchburyi clams (cockles) in northern New Zealand coastal waters. However, P. olseni has not yet been propagated in vitro from New Zealand clams. In our sample of A. stutchburyi clams from Mangemangaroa Stream, New Zealand, 24% (8/34) showed low-intensity Perkinsus sp. infections among mantle and gill tissues incubated in alternative Ray's fluid thioglycollate medium (ARFTM), and 5% (4/79) showed Perkinsus sp. lesions by histological analyses. Among clams that were screened using a polymerase chain reaction (PCR) assay, 16% (3/19) were positive for Perkinsus sp. DNA. Alternative Ray's fluid thioglycollate medium-enlarged hypnospores from tissues of five infected clams yielded three in vitro Perkinsus sp. isolate cultures that were cloned before sequencing internal transcribed spacer (ITS) regions of their rRNA gene complex. For one isolate, ATCC PRA-205, large subunit (LSU) rRNA and actin genes were also sequenced. All nucleotide sequences from all isolates consistently identified them as P. olseni, as did their in vitro cell cycles and zoosporulation characteristics. All in vitro isolate cultures and their respective monoclonal derivative strains were cryopreserved and deposited for archiving and distribution by the American Type Culture Collection (http://www.atcc.org).