Physicochemical principles and clinical results concerning the conservative treatment of kidney stones are discussed. Litholytic agents, developed over the last decades, are able to dissolve a number of kidney stones either directly through a retrograde irrigation of the kidney cavities or indirectly by using suitable drugs which can be administered orally or intravenously. Both ways of administration have their advantages and problems. The relation of chemical, physical, bacteriological, anatomical and metabolic factors to stone formation, as well as to stone dissolution and/or stone prophylaxis (metaphylaxis), is demonstrated. In addition, attention is called to the four physical factors – (1) crystallizing propensity, (2) exceeding the saturation point of the urine, (3) urine pH, and (4) ‘salting out’ effect – and their influence on stone formation. Factors promoting or preventing crystallization are classified in a biological relation. According to this ‘relation, it is theoretically possible by selective elimination of substances promoting crystallization to achieve suitable conditions for dissolving uric acid, phosphate and L-cystine stones and also to inhibit stone formation (prophylaxis/metaphylaxis). The frequency of recurrent calcium oxalate calculi can be reduced by achieving ‘anti-salting out’ conditions in human urine. These ideas were proved experimentally and in a preliminary clinical study with a limited number of kidney-stone patients.