The acidic protein hevein is the major protein in the lutoid-body fraction of rubber latex. The purified protein has a stabilising effect on suspensions of rubber particles in the presence of unfractionated lutoid-body preparations, which contain destabilising basic proteins. The hevein contents in lutoid-body fractions from rubber clones GT 1 and PR 261 are about two times higher than in that of clone LCB 1320, which may explain the faster destabilization of latex from the latter clone after tapping. Hevein and pseudo-hevein bind chitin and can be isolated by affinity chromatography on a chintin column. Pseudo-hevein binds less strongly to this material than hevein, which can be explained by a replacement of a tryptophan residue by tyrosine in the carbohydrate-binding site of the protein.