A study of the precipitation processes for sparingly soluble substances was performed with the two systems of CaSO4 . 2H(2)O and CaCO3. A continuous as well as a batch DTB-crystallizer were investigated in order to describe the influence of different operational conditions on the kinetic parameters, on the median crystal size and on the crystal modification. Besides the mode of operation the location of the feed point, the reactant concentration, the power input and the residence time were examined. The experimental results are discussed under special consideration of the mixing conditions. With the help of data from literature the results of the examined DTB-crystallizer were transferred to other types of crystallizer and to other operating conditions. In the batch experiments agglomeration and phase transformation processes play an important role. Due to the high initial supersaturation an unstable amorphous precursor was built in the case of CaCO3, which, at the end of the experiment, transferred to stable crystalline modifications. The small particle size and the high supersaturation encourage the agglomeration process compared to the continuous process.