The complementary DNAs encoding tropomyosins of the abalone Haliotis diversicolor, the scallop Chlamys nobilis, and the mussel Perna viridis were amplified by reverse transcriptase polymerase chain reaction and thereafter cloned in plasmid vectors for expression. Immunoblot analysis showed that recombinant proteins of abalone, scallop, and mussel tropomyosin were reactive to serum IgE antibodies from subjects allergic to shellfish but not to nonallergic controls. Nucleotide and amino acid sequences of abalone, scallop, and mussel tropomyosins are highly similar (mostly > 55%) to those of crustacean allergens identified as tropomyosins. Absorption experiments showed that recombinant tropomyosins from the 3 mollusks were able to remove serum IgE reactivity against the 38-kDa tropomyosin of the organisms. These results demonstrate that tropomyosin is the major allergen among various common edible mollusks. Yet a comparison between the amino acid sequences of putative epitopes in crustaceans and mollusks suggests that the epitopes in the two groups may be distinct. Parsimony analysis of the nucleotide sequences of tropomyosin from different mollusks suggests that the tropomyosin gene sequence is a useful tool for phylogenetic analysis of this group of animals.