A method for analyzing data from seeded precipitation experiments was applied. It is possible to determine the dependence of the growth rate on supersaturation by applying this model to desupersaturation data, if there is no nucleation and the crystals maintain their original shapes and densities. The suggested method was applied to desupersaturation data for probertite, NaCaB5O9. 5H(2)O, in Borax solution containing 28 wt % Na2B4O7 and crystalline probertite seeds at 368 K. The results showed that the growth rate is proportional to supersaturation. The overall rate constant was found to be dependent on the amount of seeds. This dependence can be attributed to the change of the density of precipitate during the precipitation. In the case of a small amount of crystalline seed (0.1 kg/100 kg of solution) the growth rate constants obtained from the suggested method and from the chronomal analysis show good agreement and their average value was found as 7.58 x 10(-6) kg of anhydrous probertite/(m(2).s.(kg of anhydrous probertite/100 kg of solution)).