A quinoline fluorescence method for staining zinc in axonal boutons was used to study the effects of kainic acid (KA) induced seizures upon zinc in the boutons of hippocampal mossy fibers. Compared to untreated rats, rats given KA (10-12 mg/kg) and undergoing sustained seizures showed a marked loss of zinc fluorescence in the mossy fiber regions. The reduced fluorescence was detectable within 3 h of KA administration, was most pronounced at 12-24 h, and was still noticeable up to 48 h after KA. The findings suggest that zinc is released rapidly from mossy fiber boutons during seizures.