The major storage proteins, polypeptides of 31 and 47 kilodaltons (kDa), from the seeds of cocoa (Theo= broma cacao L.), have been identified and partially purified by preparative gel electrophoresis. The polypeptides were both N-terminally blocked, but some N-terminal amino-acid sequence was obtained from a cyanogen bromide peptide common to both polypeptides, permitting the construction of an oligonucleotide probe. This probe was used to isolate the corresponding copy-DNA (cDNA) clone from a library made from poly(A) Β§ RNA from immature cocoa beans. The cDNA sequence has a single major open reading frame, that translates to give a 566-amino-acid polypeptide of Mr 65 612. The existence of a common precursor to the 31-and 47-kDa polypeptides of this size was confirmed by immunoprecipitation from total poly(A) Β§ RNA translation products. The precursor has an N-terminal hydrophobic sequence which appears to be a typical signal sequence, with a predicted site of cleavage 20 amino acids after the start. This is followed by a very hydrophilic domain of ~ 110 amino acids, which, by analogy with the cottonseed a-globulin, is presumed to be cleaved off to leave a domain of approx. 47 kDa, very close to the observed size of the mature polypeptide. Like the hydrophilic domain of the cottonseed a-globulin the cocoa hydrophilic domain is very rich in glutamine and charged residues (especially glutamate), and contains several Cys-X-X-X-Cys motifs. The cyanogen-bromide peptide common to the 47-kDa and 31-kDa polypeptides is very close to the proposed start of the mature domain, indicating that the 31-kDa polypeptide arises via further C-terminal processing. The polypeptide sequence is homologous to sequences of the vicilin class of storage proteins,