Hydrogen adsorption in microporous solid materials may enable H-2 to be stored at lower pressures than in compressed-gas tanks, and at higher temperatures than for liquid H-2. A new class of metal-organic frameworks (MOFs) with a high specific surface area appears promising for H-2 storage. Here, the H-2-uptake capacity of MOF-5 over a wide pressure range, at room temperature and at 77 K is investigated (see Figure). Adsorption of H-2 exclusively in the micropores of these metal-organic frameworks is demonstrated.