this paper gives a review on an efficient microtechnique (gel crystallization method; gcm) which quantifies crystal growth in gel matrices, and its application to research into urinary stone formation. relative crystal growth rates (vcr) of calcium oxalate hydrates (caox) were determined by simultaneous multiple measurements in 96-well microplates using computer controlled microscopic photometry. efficiency: 120 kinetic measurements/h; imprecision: $less than$ 2 at standard conditions. the method was applied to study the effects of diverse small-ionic and macromolecular constituents of human urine on the crystal growth rate of caox. the `inhibitory activity' of urine could be evaluated by comparison of the vcr measured in native and corresponding artificial samples macromolecules, at physiological concentration, played only a minor role as inhibitors in the model under regard. the gcm was employed to study the in-vivo effects of different therapeutic measures on caox growth in urine of normal volunteers. while the application of alkali citrate resulted in a $greater than$ 70 decline of vcr, no beneficial effects could be found with three magnesium compounds, and a dietary fiber preparation. in a study including 20 male recurrent caox stone formers and 29 well-matched controls, among all parameters under investigation, the vcr showed the most significant difference (p $less than$ 0.001) between the both groups. in conclusion, the method described here has been proven to be of high value with respect to a series of applications in the study of urolithiasis however, though t