GOLGI-derived coated vesicles contain a set of coat proteins of relative molecular mass 160,000 (M_r 160K; α-COP), 110K (β-COP), 98K (γ-COP) and 61K (δ-COP), and several smaller subunits¹. We have now identified and purified a cytosolic complex containing the same four coat proteins as those of Golgi transport vesicles. We term this complex the Golgi coat promoter or 'coatomer'. The coatomer also contains polypeptides of M_r 36K, 35K and 20K. It represents about 0.2% of soluble cytosolic protein. Gel filtration of unfractionated cytosol indicates that β-COP resides exclusively in the coatomer complex. The complex seems to be a likely candidate for the unassembled precursor of Golgi coated vesicles, and its purification should help investigations of the role of coat proteins in membrane budding, for which it is necessary to use a refined cell-free system.