Heneicomycin is structurally similar to efrotomycin, mocimycin (kirromycin) and X-5108 (goldinomycin). Comparisons were limited because of the small supplies available. All antibiotics show the same in vitro antibacterial spectrum although some test cultures were less sensitive to efrotomycin. Heneicomycin compared favorably with efrotomycin when given subcutaneously or per os against infections with Moraxella bovis and Streptococcus pyogenes. The rapid elimination of heneicomycin observed following oral administration may account for its poor activity against a Bordetella bronchiseptica infection where efrotomycin is effective. It appears more like X-5108 than efrotomycin biologically. The disaccharide on efrotomycin may account for the difference observed.