Nominally undoped, hydrothermally grown ZnO single crystals have been investigated before and after exposure to remote H plasma. Structural characterizations have been made by various positron annihilation spectroscopies (continuous and pulsed slow positron beams, conventional lifetime). The content of bound hydrogen (H-b) before and after the remote H plasma treatment at the polished side of the crystals was determined at depths of 100 and 600 nm, respectively, using nuclear reaction analysis. At a depth of 100 nm, H-b increased from (11.8 ± 2.5) to (48.7 ± 7.6) × 10 19 cm -3 after remote H plasma treatment, whereas at 600 nm no change in H-b was observed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.