AbstractAqueous formamide (20%) was found to exert a specific effect on the germicidal power of formic and acetic acids and also of ammonium hydroxide: bactericidal action against Bacr. aerogenes was increased six‐ to twelve‐fold. Certain other disinfecting substances were affected by formamide to a much less extent, e.g. phenols, isopropyl alcohol, acetone, oxalic acid, lactic acid, and various esters, while o‐chlorophenol and trichloracetic acid were actually diminished in germicidal activity. Possible explanations for the observed results are disc