The critical micelle concentration (cmc) of several lysophospholipids and of a lysophospholipid analogue was determined from surface tension measurements using the maximum bubble pressure method and/or 31P NMR. The use of the maximum bubble pressure method has now been extended to micromolar concentrations of surfactant, and the experimental parameters that effect its use have been explored. Surface activity was found to vary with changes in the chain length and in the headgroup polarity of the lysophospholipid. The cmc's for 1-decanoyl-, 1-dodecanoyl-, 1-tetradecanoyl-, and 1-hexadecanoyl-sn-glycero-3-phosphocholine are 7.0, 0.70, 0.070, and 0.007 mM, respectively. The cmc's for 1-decanoyl- and 1-dodecanoyl-sn-glycero-3-phosphoethanolamine are 4.4 and 0.33 mM, respectively. The cmc for dodecylphosphocholine, a lysophospholipid analogue, was found to be 1.1 mM. The cmc's for 1-tetradecanoyl- and 1-hexadecanoyl-sn-glycero-3-phosphoglycerol were found to be 3.0 and 0.60 mM, respectively, in pure water. In 0.1 M Tris-HCl (pH = 8.0), their cmc's are 0.16 and 0.018 mM, respectively. Surface tension and adsorption density values determined at the cmc are reported for each compound. The relationship of dynamic surface tension and lipid purity is discussed. These studies provide information about the micellization and interfacial properties of several biologically important lysophospholipids.