Worldwide, estuaries are under increasing pressure from numerous contaminants. This study aimed to identify a suitable marine harpacticoid copepod species for toxicity testing of New Zealand estuaries. Multiple aspects were considered for species selection and included: a broad regional distribution, ease of culture, reproductive rate under laboratory conditions, sexual dimorphism, and sensitivity to contaminants. Five species were evaluated and two (Robertsonia propinqua and Quinquelaophonte sp.) were able to be cultured. The relative sensitivity of these copepods to three reference toxicants was assessed by determining the medial lethal values following a 96 h exposure (96 h LC(50)) to these toxicants in the aquatic phase. LC(50) values for zinc, phenanthrene, and atrazine respectively were 2.0, 0.89, and 7.58 mg/L in R. propinqua and 0.64, 0.75, and 20.8 mg/L in Quinquelaophonte sp. After evaluating all factors involved in choosing a bioassay species for New Zealand, Quinquelaophonte sp. was selected as the most suitable bioassay species.