1. Mixed amides of formic and dialkyl hydrogen phosphites (dialkyl formylphosphoramidites) (alkyl=C2H5; i-C3H7; i-C4H9) were synthesized by the reaction of formamide or N-ethylformamide with dialkyl phosphorochloridites. 2. The formation of unsubstituted dialkyl formylphosphoramidites in this reaction passes through the stage of the formation of a pyrophosphorous ester and its reaction with formamide. 3. In the reaction of diethyl phosphorochloridate with formamide or substituted formamide the latter is dehydrated, and as a result of subsequent reactions tetraethyl pyrophosphate is formed. Diisopropyl phosphorochloridite reacts with formanilide analogously, and the final reaction product is the pyrophosphorous ester. 4. The reactions of some dialkyl ethylformylphosphoramidites with sulfur, nitrogen dioxide, and chloral were investigated. As a result of these reactions, the following compounds were obtained: O,O-dialkyl ethylformylphosphoramidothioates (alkyl=i-C3H7; i-C3H9), diisobutyl ethylformylphosphoramidate, and alkyl 2, 2-dichlorovinyl ethylformylphosphoramidates (alkyl=C2H5; i-C3H7; C4H9).