1. Bladder stones composed of calcium hydrogen phosphate dihydrate, calcium oxalate mono- and di-hydrate and magnesium ammonium phosphate hexahydrate (struvite) were successfully induced in rats by various dietary manipulations and by implanting zinc pellets in the bladder.
2. The effect of a diphosphonate, disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), given in the drinking water at concentrations of 0·0025, 0·05 and 0·5% (w/v), on the size and composition of these stones was examined.
3. All the concentrations of EHDP decreased the weight of the calcium oxalate calculi. In contrast, only the highest concentration of EHDP inhibited calcium hydrogen phosphate stone formation and the magnesium ammonium phosphate stones were unaffected.
4. The difference between the effects on calcium oxalate and magnesium ammonium phosphate stones is consistent with the finding that EHDP inhibited the precipitation of calcium oxalate from solution in vitro but had only a slight effect on magnesium ammonium phosphate precipitation.
5. It is suggested that EHDP might be of use in the prevention of some types of urinary stones in man.