Cost-effective metaphylaxis and monitoring is becoming more and more focused in the treatment of urinary stones. Therefore, medical practitioners are asked to reduce the analytical efforts necessary for evaluation and to control the actual biochemical risk of stone formation in the patients. The most common strategy available is based on chemical urinalysis and the calculation of theoretically derived risk parameters. However, this covers--in the best case--the analysis of the most prominent low molecular urinary constituents. No information about the fraction of the important macromolecular urinary components is obtained. Crystallization experiments in unprepared, native urine samples, carried out according to the Bonn-Risk-Index approach (BRI), allow the determination of a more realistic measure of a urine's crystallization risk since the entire urinary composition influences the experimental result. As only two parameters have to be analyzed, the BRI is a fast and cost-effective risk evaluation method. The results show a high selectivity between stone-formers and non-stone-forming persons. The changes in the BRI-risk of three calcium oxalate stone-formers after a 1 week stay in our hospital are presented and discussed in detail. In one of these patients, a follow up examination was performed in order to control the therapy's success and, additionally, to obtain information about the patient's compliance with the therapy. During hospitalization, the patients received a standardized and "stone-neutral" diet. All persons showed a distinct decrease in their individual crystallization risk.

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