A simple technique permitting long term 31P magnetic resonance spectroscopy of cultured mammalian cells is described. Cells are encapsulated in calcium alginate gels and perfused with a new phosphate‐free medium designed for maintenance of high cell viability. Intracellular pH and β‐NTP/Pi ratios, studied in three cell types, remained stable over a 16–20 h NMR monitoring period. The techniques described may be useful for monitoring cell metabolism with a variety of cell types. Copyright © 1990 John Wiley & Sons, Ltd.