The novel fatty acids 16-methyl-6(Z)-heptadecenoic acid and 16-methyl-8(Z)-heptadecenoic acid were identified for the first time in nature in a species of the bacterium Micrococcus isolated from Lake Pomorie in Bulgaria. The principal fatty acids in this bacterium were a series of iso-anteiso fatty acids with chain lengths between C(14) and C(24), while the most interesting series of monounsaturated fatty acids was a family of Delta(6) fatty acids with chain lengths between C(14) and C(17). The novel compounds were characterized using a combination of GC-MS and chemical transformations, such as dimethyl disulfide derivatization and catalytic hydrogenation. The results established for the first time a bacterial origin for some of these Delta(6) fatty acids.