The effect of inorganic pyrophosphate analogues on the enzymic activity of inorganic pyrophosphatase from E. coli was studied. Hypophosphoric and diphosphonic acids were shown to inhibit inorganic pyrophosphatase, whereas pyrophosphorous acid exerts almost no effect on the hydrolysis of inorganic pyrophosphate. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.