Membranes are composed of hundreds of distinct kinds of phospholipids, and the types of lipids that are found within a membrane bilayer impact its biophysical properties including its fluidity, permeability and susceptibility to damage. Our primary interest is in understanding the mechanisms that control the phospholipid composition and that preserve the membrane over time. We use stable isotope tracing strategies and mass spectrometry to quantify phospholipid abundance and dynamics in the model organism, C. elegans.