A total of 459 specimens covering 51 species in 9 families was collected from October 1992 to May 1996 in Taiwan. All specimens were assayed for the presence of tetrodotoxin (TTX) and paralytic shellfish poison (PSP). The specimens of five xanthid crabsZosimus aeneus, Lophozozymus pictor, Ategatopsis germaini, Atergatis floridus, andDe‐mania reynaudiwere found to contain potent toxins. Among them,A. germainishowed the highest toxicity. The toxin profile of each toxic crab species was as follows: 82% TTX and 18% PSP in Z.aeneus, 89% TTX and 11% PSP inL.pictor, 3% TTX and 97% PSP inAgermaini, 85% TTX and 15% inA. floridus, and 88% TTX and 12% PSP inD. reynaudi. PSP was mainly composed of gonyautoxins (GTXs) 1–4 in Z.aeneus, L. pictor, andA. floridus, but GTX 3 and hydroxysaxitoxin inA. germaini, and neosaxitoxin inD. reynaudi. The PSP‐producing dinoflagellate planktonAlexandrium minutumand TTX‐producing bacteria includingVibrio alginolyticusandVibrio parahaemolyticuswere isolated and considered as the sources of the toxins.