Cats fed a semipurified diet containing casein as the source of protein develop taurine deficiency. In order to establish whether this had an adverse effect on bile, kittens and adult cats were fed the casein diet or that diet with a supplement of taurine, cystine, or methionine, and gall bladder bile was characterized for its taurine-glycine conjugation and the cholesterol: phospholipid: bile acid ratio. The data indicate that cats conjugate their bile acids almost exclusively with taurine, and though plasma and retinal pools of taurine are largely depleted by feeding the casein diet, the conjugation of bile acids is only moderately affected. A major conversion to glycine conjugation did not occur, but free cholic acid did increase with decreased taurine conjugation. Dietary supplements of methionine or cystine, precursors of taurine, failed to satisfy the taurine requirement for bile acids in kittens whereas methionine appeared to satisfy this requirement in adult cats. The cholesterol: phospholipid: bile acid profile was not appreciably altered by these dietary circumstances. It would appear that kittens may require dietary taurine and that taurine pools in cats may be biologically independent of one another.