Muon spin relaxation of two liposome samples consisting of 100% DPPC (dipalmitoylphosphatidylcholine) and 50:50mole% DPPC:Cholesterol at a final lipid concentration of 100mg/mL are compared. The observation of a significant loss in the muonium fraction from 11% to 6% when cholesterol is present is compatible with radical formation in the second sample. Also reported are measurements on pure solid cholesterol where a clear T 1 minimum at ca 100K, corresponding to a dynamic process with activation energy of ca. 1.89kJmol −1 and an attempt frequency of 5.89×10 10 s −1 , is observed. An estimate of a hyperfine interaction of 255.4MHz for this radical predicts a ΔM=1 ALC transition at 0.94T.