Brain sections incubated in vitro with alpha-[3H]kainic acid (KA; spec. act. 62.5 Ci/mmol), reveal a heterogeneous distribution of low and high affinity KA binding sites in the brain. The highest density of KA binding sites was localised to the hippocampus CA3 region and to superficial layers of the entorhinal cortex (3.8-6.0 mu Ci/g tissue). Intravenous injection of [3H]KA (1 mu Ci/g) reveals limited overall penetration of [3H]KA across the blood-brain barrier. However, a dense labelling of the hippocampus, entorhinal cortex and lateral septal regions (2.5-3.8 mu Ci/g tissue) was observed. Behaviourally, these rats exhibited mild limbic seizure activity possibly as a result of a direct action of KA in the hippocampus or entorhinal cortex.