A 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 (M(r) = 3,298 for the mono-sodium salt). Maitotoxin-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 (M(r) = 1,060.5 for the disodium salt). Brevetoxin-A ([M+H]+ m/z = 867.5) and brevetoxin-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.(ABSTRACT TRUNCATED AT 250 WORDS)