The sodium-independent binding of taurine and GABA were determined with mouse brain membranes subjected to various freezing-thawing cycles, washing procedures and Triton X-100 treatments. The treated membranes were characterized by electron microscopy and determination of their content of endogenous free amino acids, e.g., taurine, GABA, glutamate, aspartate and glycine. The washings and the detergent gradually disrupted all synaptic structures, yielding empty-looking sealed membrane pouches of various sizes. Only traces of taurine, GABA, aspartate and glutamate were present in the Triton X-100-treated membranes, whereas these membranes still contained some glycine. Concomitantly, the affinity and maximal capacity of GABA binding increased, indicating that the treatments progressively removed some endogenous GABA binding inhibitors. Saturable taurine binding became detectable only after the Triton X-100 treatment, endogenous taurine, removable from membranes only with difficulty, obviously hampering binding measurements.