When pyridine (PYR) is added to powdered Wyodak subbituminous coal (WYO), the sample is converted to a paste, and the molecular-level adduct which is formed is stable for months. After the excess pyridine has evaporated from the WYO−PYR sample, the stoichiometry of the adduct is ca. two pyridine molecules per bilayer of WYO polycyclic units; this adduct exists even after mild vacuum treatment of the sample. The pyridine molecules in this adduct appear to be located between the bilayer lamellae and to be H-bonded to either H−O or H−N moieties attached to the poly-cyclic aromatic units of WYO. An H-bonded N- - -H−X distance of 2.6 A has been calculated from a structural model of the WYO−PYR adduct.