Tumors and transformed cells have been shown by 31P NMR to contain elevated concentrations of two phosphomonoesters, phosphorylcholine and phosphorylethanolamine, involved in phospholipid metabolism. In order to understand the biochemical basis for these phenomena new methods are needed to allow for analysis of the relevant metabolic pathways in intact cells. One such promising tool may be phosphonium-choline, a 31P NMR-visible analog of choline in which the trimethyl-ammonium group of choline has been replaced with a trimethyl-phosphonium moiety. As shown previously [Sim et al. Biochem. J. 154, 303 (1976)], this compound is non-toxic and readily metabolized by cultured cells into phospholipids. In this paper we describe in greater detail some of the chemical and NMR spectroscopic properties of this material. Most significantly we show here that the chemical shift of phosphonium-choline is sensitive to the phosphorylation state of the analog and that the phosphonium nucleus is NMR-visible even after its incorporation into phospholipid. The unique properties of this analog should make it possible to use high-field 31P NMR to follow the flux of phosphonium-choline through the Kennedy pathway in intact perfused cells cultures.