Solutions, based on calcium chelating agents, with excellent prospects as litholytic agents in vitro were tested on toxicity to the mucosa of the bladder of the rat. The following compounds were tested at a concentration of 12.5 mM., buffered with triethanolamine 0.2 M at pH 8 and 8.5: ethylenediaminetetra acetic acid with as cation H2+, Li+, Na+, K+, and Cs+, trans-cyclohexane-1.2 diaminetetra acetic acid (cations H+, Na+, K+), diethylenetriamine penta acetate (cations H+, Na+, K+), disodiumethyleneglycol-bis (2 aminoethyl) tetra acetic acid and disodium hydroxyethylethylenediamine tetra acetate. All agents were found to be very noxious to the bladder mucosa of the rat and are unlikely to be safe for clinical use.