Abstract The i.r. spectra of methanol—ammonia and methanol—triethylamine systems in the solid state are reported, and the internal modes of CH 3OH · NH 3, CH 3OD · ND 3 and CD 3OD · ND 3 and the OH(D) stretching of (methanol) n · triethylamine ( n = 1 or 2) are assigned. The OH(D) stretching in the former system is lower, about 360 (190) cm −1, than that in the latter one. This abnormal behavior is explained by the hydrogen bond formed among methanol · ammonia species, resulting in the polymeric chain structures. The OH(D) stretching of those systems has some structure, which is explained by Fermi resonance between the fundamental and the first overtone or the combination of the OH(D) in-plane bending.