The mechanism and kinetics of choline transport and phosphorylation in MCF7 human breast cancer cells was studied by 31P, 13C and 2H NMR, applying the zero trans method. Choline was transported by a Michaelis-Menten like mechanism with a maximum transport rate T(max) = 13.5 +/- 2.6 nmol/hour/mg protein (3.06 +/- 0.6 fmol/cell/hour) and choline concentration at half maximal transport rate of Kt = 46.5 +/- 2.8 microM. The rate of choline phosphorylation was more than two orders of magnitude faster than the rate of its transport (T(max)) maintaining the ratio [phosphocholine]/[choline] higher than 100. The results demonstrated enhanced choline transport and choline kinase activity in breast cancer cells.