CHEMICAL1 and enzymic2 studies from these two laboratories suggested that coenzyme A is best represented by formula (I) (cf. ref. 3). While the synthesis of various fragments of the molecule4 has lent considerable support to this structure, the enzymic and chemical evidence did not agree on one point. This concerned the nature of a substance obtained by the action of nucleotide pyrophosphatase on the coenzyme and which stimulated the growth of Acetobacter suboxydans5. Although not isolated in a chemically pure state, it was thought to be a simple phosphate of pantothenic acid6. None of the synthetic pantothenic acid phosphates showed activity towards this organism ; consequently, it was suggested1 that this ‘Acetobacter-stimulatory factor’ might be pantetheine-4′phosphate (II). An unambiguous synthesis of (II) is described here.