This paper reports a physicochemical investigation of the effect of titanocenes on hydroxyapatite crystallization in vitro. The experimental conditions resemble the physiological, at sustained supersaturation employing the constant composition method. All titanocene dihalides were found to inhibit crystal growth of hydroxyapatite, possibly through adsorption of the chloride hydrolysis products on the active growth sites. It is suggested that the growth mechanism is probably surface-diffusion-controlled spiral growth. To explain the inhibiting activity of the titanocenes, the relation of the organometallic compound stereochemistry and the crystal surface characteristics is extensively discussed.