Gallium chloride in solution at concentrations of 10-100 microM inhibits the seeded growth of hydroxyapatite from metastable calcium phosphate solutions. Using initial rate data, an effective rate constant for the process of crystal growth can be derived; this rate constant varies with gallium concentration in a log-dose/response fashion. The disappearance of gallium occurs disproportionately fast in the early stages of the experiments. This suggests that gallium acts by adsorbing to the crystal surface where it inhibits crystal growth.