Tablets comprising isotopic urea and an inorganic compound. Tableting a mixture of the urea with one or more inorganic compounds (additives) can inhibit the adhesion due to cohesiveness of urea and can give tablets having a practical disintegration time and sufficiently high hardness. The tablets are useful for the diagnosis of infections with urease-producing microorganisms containing isotopic urea, particularly the one with Helicobacter pylori.