We have used the taurine analogue, β-alanine, to perturb the taurine concentrations in taurine-supplemented and taurine-deprived adult cats. By using 5 % β-alanine in the drinking water for 20 weeks, both groups of cats had greatly reduced brain taurine concentrations. Taurine-supplemented cat brain accumulated relatively small amounts of β-alanine whereas taurine-deprived cats accumulated large amounts of β-alanine. The cerebellum of cats treated with β-alanine had a number of pathological changes compared with similar cats drinking water alone. The changes were more severe in the taurine-deprived cats, and included reduced numbers of granule and Purkin je cells, with many of those remaining appearing pyknotic and dying. Long swollen fibers were seen in the white matter, resembling Rosenthal fibers described in some human cerebellar diseases. There was also prominent gliosis. Using antibodies to β-alanine and taurine, β-alanine was localized in Purkinje cell soma and dendrites, in Golgi II cells, and in some granule cells, especially in taurine-deprived cats treated with β-alanine. Taurine appears to have been virtually eliminated from Purkinje and granule cells, and concentrated in Golgi II cells and glia. We conclude that β-alanine is responsible for these neuro toxic pathological changes. © 1996 Wiley-Liss, Inc.