We studied some pharmacological properties of dimephosphone P—C and aza analogs, viz., dimethyl (2-methyl-4-oxopent-2-yl)phosphonate, which is one of the first organophosphorus drugs having no anticholinesterase activity. Replacement of two P—O—C fragments in dialkyl (2-methyl-4-oxopent-2-yl)phosphonates with the P—C ones on going to dialkyl-(2-methyl-4-oxopent-2-yl)phosphine oxides results in a dramatic decrease in the acute toxicity of the latter to warmblooded animals. The toxicities of dimephosphone aza analogs and (γ-oxoalkyl)phosphine oxides under study depend on the nature of aza fragment introduced instead of the oxygen atom. Dimephosphone pyridinoylhydrazones were found to exhibit a high antiinflammatory activity, which increases the interest for this type compounds as promising tuberculostatics.