Corynebacterium sp. produced antibacterial substances (corynecins) when an n-paraffin mixture was used as the sole carbon source. Structures of the substances were determined as acyl derivatives of D-(-)-threo-1-p-nitrophenyl-2-amino-1,3-propanediol (free base of chloramphenicol). In the course of screening for antibacterial substances, it was found that Corynebacterium sp. grown on an n-paraffin mixture (C₁₂-C₁₈) as the sole carbon source produced a mixture of antibacterial substances (corynecins) in the aqueous layer of the culture medium. Three components (I, II and III) showed antibacterial spectra similar to chloramphenicol, while the others (IV and V) had no activity. IR and NMR spectra indicated a structural correlation with chloramphenicol, with common groups including hydroxyl, amide, nitro and 1,4-disubstituted phenyl. Corynecin-I, II, IV, and V were hydrolyzed by methanolic hydrochloride to yield the same crystalline hydrochloride, identified as D-(-)-threo-1-p-nitrophenyl-2-amino-1,3-propanediol hydrochloride (free base of chloramphenicol). Based on spectral data, molecular formulas, and optical rotations, the structures of corynecin-I (acetyl derivative), II (propionyl derivative), III (isobutyryl derivative), IV and V (acetate derivatives) were established. The absolute configurations of all corynecins were confirmed, and corynecin-III and V were new compounds.