Confocal laser-scanning microscopy images of a giant unilamellar phospholipid vesicle (GUV). The lipid composition of this GUV was DPPC/DLPC = 1/1, with DiIC20(3) and ß-BODIPY FL C5-HPC (D3803) dyes at mole fraction ~0.001. Excitation was at 488 nm. The upper right image is the fluorescence emission through a 585 nm longpass filter, thus almost exclusively from DiIC20(3). The upper left image is the emission through a 522 ± 35 nm bandpass filter, thus almost exclusively from ß-BODIPY FL C5-HPC. The bottom image is color-merged, using the public domain NIH Image program. Image contributed by Gerald W. Feigenson, Cornell University, and reprinted with permission from Biophys J (2001) 80:2775.