A neuroblastoma cell culture assay was used to analyze shellfish extracts for presence of paralytic shellfish poisoning toxins (saxitoxins). Results were compared with mouse bioassays performed as part of a screening program for shellfish toxins in New Zealand. Twenty-nine samples gave negative results in both assays. Fifty-seven samples gave positive results in at least one assay. The correlation between the assays for saxitoxin equivalent levels in shellfish was 0.867. In spiking studies on shellfish extracts, the neuroblastoma assay showed a good response to added saxitoxin. Although these results support use of the neuroblastoma assay as a screening procedure for shellfish toxicity, results close to regulatory limits should be confirmed by mouse bioassay.