Rubber (cis-1,4-polyisoprene), an important raw material for many industrial uses, is synthesized in the latex of Hevea brasiliensis (Willd. ex A.Juss) Mull. Arg. We postulated that the genes uniquely or preferentially expressed in the latex may be important for rubber biosynthesis. We constructed cDNA libraries from the latex of H. brasiliensis to investigate the genes expressed in the latex by single-run partial sequencing of the cDNA clones. Sequence analyses identified 245 expressed sequence tags (ESTs), of which 57;showed homology to previously described sequences in public databases. About 16;of the database-matched ESTs encode rubber biosynthesis-related proteins such as rubber elongation factor(REF) and small rubber particle protein(SRPP). The second most frequent transcripts next to rubber biosynthesis-related genes were defense genes and protein metabolism-related genes (12.6;each). About 27;of the database-matched ESTs had sequence homology with genes of unknown function. Among the redundantly expressed genes, REF was the most frequently expresed(6.1;), followed by SRPP(3.7;) and HbLAR(2.9;). Northern blot analyses showed that ten(71;) of the 14 ESTs studied were expressed at a higher level in latex than in leaves.