Background Given the recent detection of TTX in bivalve molluscs but the absence of a full collaborative validation study for TTX determination in a large number of shellfish samples, interlaboratory assessment of method performance was required to better understand current capabilities for accurate and reproducible TTX quantitation using chemical and immunoassay methods. Objective The aim was to conduct a collaborative study with multiple laboratories, using results to assess method performance and acceptability of different TTX testing methods Methods Homogenous and stable mussel and oyster materials were assessed by participants using a range of published and in-house detection methods to determine mean TTX concentrations. Data was used to calculate recoveries, repeatability and reproducibility, together with participant acceptability z-scores. Results Method performance characteristics were good, showing excellent sensitivity, recovery and repeatability. Acceptable reproducibility was evidenced by HorRat values for all LC-MS/MS and ELISA methods being less than the 2.0 limit of acceptability. Method differences between the LC-MS/MS participants did not result in statistically-different results. Method performance characteristics compared well with previously-published single-laboratory validated methods and no statistical difference was found in results returned by ELISA in comparison with LC-MS/MS. Conclusions The results from this study demonstrate that current LC-MS/MS methods and the ELISA are on the whole capable of sensitive, accurate and reproducible TTX quantitation in shellfish. Further work is recommended to expand the number of laboratories testing ELISA and to standardise an LC-MS/MS protocol to further improve interlaboratory precision. Highlights Multiple mass spectrometric methods and a commercial ELISA have been successfully assessed through collaborative study, demonstrating excellent performance.