Fluoropyrimidine chemotherapy relies on the intracellular anabolic conversion of 5‐fluorouracil and the corresponding nucleosides to cytotoxic fluorinated nucleotides (F‐Nuctd), such as 5‐fluorouridine‐5′‐triphosphate (FUTP) or 5‐fluoro‐2′‐deoxyuridine‐5′‐monophosphate (FdUMP), which can be detected by 19F‐NMR spectroscopy. We have made 19F‐NMR signal assignments at 11.7 T and 4 °C for model solutions containing 5‐fluorouracil (FUra), 5‐fluorouridine (FUrd), 5‐fluoro‐2′‐deoxyuridine (FdUrd), 5‐fluorouridine‐5′‐monophosphate (FUMP), FdUMP, 5‐fluorouridine‐5′‐diphosphate (FUDP), FUTP and 5‐fluorouridine‐5′‐diphospho(1)‐α‐D‐glucose (FUDPG), and we have studied the effects of pH over the range 4.5–7.8, of Mg2+ concentration and addition of EDTA. This information provides a basis for the analysis of 19F‐NMR spectra obtained from cells, tissues or extracts following fluoropyrimidine treatment. Copyright © 1999 John Wiley & Sons, Ltd.