A low resolution solution structure of the cytokine interleukin-1β, a 153 residue protein of molecular weight 17,400, has been determined on the basis of 446 nuclear Overhauser effect (NOE) derived approximate interproton distance restraints involving solely NH, C αH and C βH protons, supplemented by 90 distance restraints for 45 hydrogen bonds, and 79 φ torsion angle restraints. With the exception of 27 C αHC αH NOEs, all the NOEs were assigned from a three-dimensional 1H 1H NOE 15N 1H heteronuclear multiple quantum coherence (HMQC) spectrum. The torsion angle restraints were obtained from accurate 3 J HNα coupling constants measured from a HMQC-J spectrum, while the hydrogen bonds were derived from a qualitative analysis of the NOE, coupling constant and amide exchange data. A total of 20 simulated annealing (SA) structures was computed using the hybrid distance geometry-dynamical simulated annealing method. The solution structure of IL-1β comprises 12 β-strands arranged in three pseudo-symmetrical topological units (each consisting of 5 anti-parallel β-strands), joined by turns, short loops and long loops. The core of the structure, which is made up of the 12 β-strands, together with the turns joining strands I and II, strands VIII and IX and strands X and XI, is well determined with a backbone atomic root-mean-square (r.m.s.) distribution about the mean co-ordinate positions of 1.2(± 0.1) Å. The loop conformations, on the other hand, are poorly determined by the current data. A comparison of the core of the low resolution solution structure of IL-1β with that of the X-ray structure indicates that they are similar, with a backbone atomic r.m.s. difference of only 1.5 Å between the co-ordinates of the restrained minimized mean of the SA structures and the X-ray structure.