Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the as-sputtered films were placed under hydrothermal conditions in distilled water solutions at pH 5.0, 7.0 and 9.0 and 110 degrees C. The crystallinity, the Ca/P ratio, thickness, and the surface of the films were observed using XRD, EDS, and SEM, respectively. The as-sputtered film was crystallized in distilled water at varying pH after the hydrothermal treatment, and the crystallinity of the film increased with treatment time. The HA crystal size increased with pH. At pH 5.0, beta-TCP was produced as well as HA. The Ca/P ratio of the film decreased with increasing treatment, and the ratio at pH 9.0 was 1.74 after 48 h, while in pH 5.0 and 7.0 it was 1.63. After hydrothermal treatment, the film remnant ratio increased with pH, with 75.9, 82.4 and 91.7% of the film remaining after 48 h at pH 5.0, 7.0 and 9.0, respectively. (C) 2005 Springer Science + Business Media, Inc.