9-(2-Anthryl)-nonanoic acid, a newly synthesized photoactivable molecule, is shown to be incorporated into the membrane lipids of the bacterium Micrococcus luteus, through the regular metabolic pathway. This incorporation, which occurs at the sn-1 position exclusively and without any degradation or elongation of the anthracene fatty acid, is accompanied by an upward shift of the chain length of the other fatty acids.