The lateral diffusion coefficient of 5-N-(octadecanoyl) aminofluorescein (ODAF) in the interfacial layer of foam films of different characteristic thicknesses stabilized by a range of phospholipids was measured by the fluorescence recovery after photobleaching technique. The diffusion coefficient of ODAF in approximately 100-nm-thick equilibrium films is approximately fivefold greater than that of ODAF in the black films due to the absence of short-range interactions normal to the interfaces in the thick films. The diffusion coefficients of ODAF in common black films are higher than those of ODAF in Newton films composed of the same lipid(s) due to the absence of an interlamellar solvent layer between the monolayers and the specific properties of the latter films. Significant hysteresis in the diffusion coefficient was observed during temperature cycling. The character and area of the hysteresis curves obtained were consistent with the lipid in the foam him maintaining the diffusion properties characteristic of the higher temperature state due to a relaxation time longer than the equilibration time allowed in the hysteresis experiment.