The rotational spectra of two conformers of 1,4-butanediol have been assigned by pulsed-jet Fourier-transform microwave spectroscopy. Both species display an intra-molecular OH center dot center dot center dot O hydrogen bond. For the most stable conformer, the rotational spectra of four isotopologues (OH-OH, OD-OH, OH-OD and OD-OD) have been measured. The mu(a)-type transition of its two symmetric species, OH-OH and OD-OD, are split into two evenly spaced component lines separated by 6.292(1) and 0.0137(5) MHz, respectively. These splittings are due to the concerted internal rotation of the two OH (or OD) alcoholic groups, which connects two equivalent minima. A partial r(s) structure has been obtained. (C) 2012 Elsevier B. V. All rights reserved.