The electrolytic calcium phosphate coatings have been deposited on titanium at room temperature and presented several differences with respect to other documented reports. The present study aimed to investigate the immersion behaviors of the uncoated titanium, the hydroxyapatite ( HA) coated and the dicalcium phosphate dihydrate (DCPD) coated in the simulated physiological fluid (Hank's solution) at 37degreesC for 1, 7, 14, and 30 days. For the evaluation in dissolution or precipitation, morphology, composition, and crystal structure, the specimens were characterized by weight variation, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy before and after immersion. The plate-like DCPD structure was not stable in Hank's solution. However, its dissolution revealed the enhancing effect on the precipitation of newly formed hydroxyapatite. The calcium deficient hydroxyapatite (CDHA) can be conducted directly by the HA as-coated or the HA500 (annealed at 500degreesC, Ca/P = 1.63), or indirectly by the DCPD coated (Ca/P = 1.58), but not by the HA700 (annealed at 700degreesC, Ca/P = 1.80). The newly formed granular hydroxyapatite showed the more crystallization than the as-coated. Besides, the annealing enhanced the crystallization of the as-coated hydroxyapatite. Generally, the electrolytic CaP coating including the DCPD coated, HA as-coated, HA500, and HA700 specimens played an important role on the precipitation of newly formed hydroxyapatite in Hank's solution, but the uncoated Ti did not. (C) 2004 Kluwer Academic Publishers.