Pontine nuclei dissected from rat brain slices released previously accumulated D-[3H]aspartate (D-Asp) and [14C]gamma-aminobutyrate (GABA) Ca-dependently when exposed to 50 mM K. These efflux rates were substantially increased by including 0.5 mg/ml bovine serum albumin in the superfusion fluid. Degeneration of the cortico-pontine fibres 5 days after cutting the crus cerebri caused an 80% reduction in the fractional rate of Ca-dependent D-Asp release and a 60% reduction in uptake. The fractional rate of GABA efflux was significantly less reduced than that of D-Asp efflux, and GABA uptake was nearly unchanged.