Paralytic shellfish toxins of two clonal cultures of Alexandrium minutum isolated during the 1993 toxic shellfish events in the Bay of Plenty, New Zealand, were analyzed using high-performance liquid chromatography. Toxin composition profiles of both cultures showed neosaxitoxin (> 65 mole%) as the principal toxin, with saxitoxin and gonyautoxins (GTX1-4) as minor components. Neither C-toxins (C1-4) nor GTX5-6 were detectable in the two isolates. Bay of Plenty isolates of A. minutum have a unique toxin profile not found in any other isolates of this species that have been characterized. This weakens the hypothesis that A. minutum was recently introduced to New Zealand waters by ballast water or other long-distance transport mechanisms, and argues instead that the species was endemic to the area, but not noticed in the past. The average toxicity of the cultures was 8.8 and 11.0 pg saxitoxin equiv. cell-1 with acetic acid or HCl extraction, respectively. These are at the high end of the range of toxicity reported for A. minutum strains from around the world, and on a cell volume basis are comparable to the most toxic strains of the Alexandrium tamarense group. The toxin profile of A. minutum most closely matches that of mussels and to a lesser degree tuatua harvested from the Bay during the 1993 outbreak, but is quite different from the profile measured in scallops and pipi. Plausible mechanisms for bioconversion of the ingested algal toxins within the latter two shellfish species can be proposed, but it seems more likely that either other strains of A. minutum or other saxitoxin-producing dinoflagellates were ingested by those shellfish. This study established that A. minutum from the Bay of Plenty contains saxitoxins, has a unique toxin composition compared to all other isolates of this species, and was responsible for at least part of the PSP toxicity measured in shellfish during the 1993 outbreak.