The neuroblastoma assay measures the extent to which the voltage-activated sodium channel is open. Shellfish contamination by saxitoxins and brevetoxins, which act through their effect on these sodium channels, can potentially be measured using this assay. It is an effect-based assay. That is, it measures the overall toxicity, and does not rely on knowing which toxin variants are present. We are evaluating the neuroblastoma assay as a potential replacement for the mouse bioassay in the monitoring programme for New Zealand shellfish. Sample preparation methods and neuroblastoma assays for the determination of brevetoxins and saxitoxins from shellfish are briefly described. The brevetoxin method can also be applied to the determination of ciguatoxins in fish samples. These assays have been applied to a variety of shellfish samples and the results compared with mouse bioassay. The assays were capable of detecting both brevetoxins and saxitoxins present in shellfish at levels below the regulatory limit. Gymnodimine, a sodium channel active compound which is not orally toxic, was not detected in either assay as it was separated from the toxins during sample preparation.Ciguatoxins were detected in three of four imported fish samples where ciguatoxins were suspected of causing illness. Brevetoxins were detected in only two of five supposedly NSP positive samples. Of the remaining samples, two contained sufficient yessotoxin to explain the observed toxicity. The fifth sample contained gymnodimine plus some underlying toxicity. This underlying toxicity was not identified. Saxitoxins were reliably detected in all PSP positive samples tested. The result to date indicate that these assays are suitable to replace the mouse bioassay in the detection of sodium channel active compounds. Further validation work for these assays is in progress.