Kainic acid (KA) is now being widely used in neurobiology as a lesioning tool but, until recently, no neurohistological studies had been done on rabbits. The present study was undertaken to investigate the effect of kainic acid on hippocampal and caudate neurons in adult and young rabbits.Our results were as follows:1. Intraventricular injection of 0.8 ?g of KA caused destruction of the most of pyramidal cells in CA_3 and CA_4 in adult rabbits. At the same time damage to caudate neurons was also observed. After injection of 0.3 of 0.5 ?g of KA approximately one half of neurons in CA_3 and CA_4 was destroyed. Injection of KA with higher dose (1 ?g) caused more extensive damage to hippocampal neurons. However, after intraventricular injection of KA (0.1 or 0.2 ?g) in young rabbits (15～18 days old), the damage to some pyramidal ceils was observed only in CA_3a.2. Injection of 0.3 ?g KA into rabbit hippocampus caused destruction of neurons confined to the injected area. Intracaudate injection of KA with same dose (0.3 ?g) caused a small loss of caudate neurons, and the damage seemed less extensive.It was suggested that given proper care, KA can be also used to lesion selectively most perikarya in rabbit brain area.