AbstractUrinary bladders from the desert tortoises,Testudo graecaandGeochelone carbonariawere removed at specific times during the year and studied by electron microscopy. Three epithelial cell types were found in both species in all bladders examined: (1) granular cells, (2) mitochondria‐rich cells, and (3) basal cells. Cells analogous to these three types have also been observed in amphibian bladders (from to adBufo marinusand bullfrog,Rana catesbiana) and reptilian bladders (fromPseudemys scriptaandClemmys caspica). Both tortoises have an incomplete layer of basal cells so that the granular and mitochondria‐rich cells extend from the lumen to the basement membrane: some thing not observed in bladders from bullfrog or turtles. A flask‐shaped light cell was observed in theGeochelone carbonariabladder obtained in April. No counterpart of this cell was seen in the same species sacrificed in January, or in any of theTestudo graecabladders, although a similar cell has been described in the turtle,Pseudemys scripta(Rosen, Expt. Molec. Path.,12: 286–296, 1970). This study was undertaken to characterize the cell types present in tortoise bladder and to compare them with cell types in the bladder of the turtle, bullfrog a