Ten strains of Lautropia mirabilis (ATCC 51599(T) and nine phenotypically similar clinical isolates) were examined for cellular fatty acid (CFA) composition to evaluate their chemical relatedness to known bacterial species and groups. The CFAs were liberated from whole cells by base hydrolysis, methylated, and analyzed by gas-liquid chromatography. CFA profiles were generated by using a commericial software package (MIDI, Newark, Del.). All strains tested had an identical CFA profile characterized by major amounts of 16:1omega7c (41%) and 16:0 (44%); smaller amounts (1 to 4%) of 3-OH-10:0, 12:0, 14:0, 15:0, and 18:1 omega7c; trace amounts (<1%) of 10:0, 18:2 and 18:0; and no cyclopropane acids. This profile was similar to the CFA profiles of Acidovorax delafieldii, Comamonas terrigena, and strains of an unclassified Centers for Disease Control group designated weak oxidizer group 1. CFA analysis, when supplemented by phenotypic characterization, is useful for the identification of L. mirabilis isolates.