The knowledge of rodent parasites and their distribution are important in every country as many of these threaten both human and domestic stock populations either directly or by the diseases transmitted by them. Although the parasites of the rodent species present in New Zealand have been widely studied overseas, the introduction of rodents into New Zealand from a variety of sources has meant that the faunal assemblage infesting these hosts could not be predetermined. The long associations of all four rodent species with man, and his role in their introductions to New Zealand have meant that the normal patterns of zoogeography cannot be expected to operate in the distribution of rodent parasites. Information on the metazoan parasites of rodents in New Zealand is not extensive. Smit (1965) summarized most of the known flea distributions, Ford-Robertson and Bull (1966) published some information on parasite collections made from Rattus exulans on Little Barrier and Hen Islands and Blakelock and Allen (1959) listed several parasites of Rattus rattus and Rattus norvegicus in the Wellington area. There are several isolated records of mite (Acarina) species occurring on rats and mice and these have been summarized by Whitten (1962), Sweatman (1962) and Spain and Luxton (1971). Beveridge and Daniel (1965) listed two parasite species from Rattus norvegicus and Cairns (1966) recorded the distribution of Trichinella spiralis (Nematoda) in R. norvegicus. No extensive survey of the parasites of any of the rodent species in New Zealand has previously been published so for this project all four rodent species were collected from as wide a range of localities and habitats as possible. The distributions and incidence of the parasites collected along with the factors influencing them are examined while the relevance of the parasite fauna both biologically and economically and possible reasons for the composition of the fauna are also considered.