AbstractA range of marine polyether toxins from dinoflagellates were analysed by ionspray mass spectrometry. Ciguatoxin‐1 ([M + H]+ m/z = 1,111.8) purified from several fish species yielded singly charged ions corresponding to the parent ion, sodium and H2O adducts and ions for the loss of up to five H2O molecules. Ciguatoxin‐1 was detected to 1 ng; however, interference from fish lipids precluded direct detection of ciguatoxin‐1 in crude extracts from fish flesh spiked with ciguatoxin‐1 at a level equivalent to 1.5 ng ciguatoxin‐1/g of extracted flesh. Maitotoxin‐2 yielded doubly and triply charged ions for sodium and potassium salts and likely possessed only one sulphate ester (Mr = 3,298 for the mono‐sodium salt). Maito‐toxin‐3, a recently isolated small maitotoxin, yielded singly charged ions including ions for the loss of one sulphate and up to four H2O molecules. Maitotoxin‐3 is proposed to be a polyether compound possessing two sulphate esters (Mr = 1,060.5 for the disodium salt). Brevetoxin‐A ([M + H]+ m/z = 867.5) and bre‐vetoxin‐B ([M + H]+ m/z = 895.5) yielded singly charged ions corresponding to the parent ion, Na+ adducts and the loss of up to four H2O molecules. Okadaic acid ([M + H]+ m/z = 805.5) yielded singly charged ions corresponding to the parent ion and ions for the loss of up to three H2O molecules. A signal for M + 18 Da species that may represent [M + NH4]+ was observed for ciguatoxin‐1, brevetoxin‐A and ‐B, and okadaic acid. For all polyethers examined, the orifice potential influenced the relative intensity of the ions detected in a predictable manner. lonspray mass spectrometry provides a simple, sensitive means of identifying a range of marine polyether toxins, with the potential to form the basis of confirmatory assays for such toxins. © 1994 Wiley‐Liss, Inc.