THE linker histone H1 binds to the nucleosome and is essential for the organization of nucleosomes into the 30-nm filament of chromatin(1). It has been implicated in the repression of transcription(2,5), and phosphorylation of H1 may be involved in cell-cycle-dependent chromatin condensation and decondensation(6). A long-standing issue concerns the location of H1 in the chromatin filament(7). The original solenoidal model(8) proposes that H1 is inside the 30-nm filament, but other models, also helical, suggest a variable(9) or more accessible(10) location for H1. Investigations to determine the location of the linker histone based on its accessibility to antibodies(11-15) or immobilized proteases(16) under various ionic conditions have yielded conflicting results. Here we use neutron scattering in a direct structural determination to show that H1 is located in the interior of the filament.