Rats Krushinsky-Molodkina inbred strain (KM) genetically prone to audiogenic seizures were injected with pineal hormone melatonin (50 mg/kg, s.c.) within the period 7th to the 14th posnatal days (PND). The remote effects of this injection adult KM rats consisted in a decrease in the latency and increase in severity of myoclonic seizures produced by audiogenic kindling (20 sound stimuli, 100 dB and 12-15 kHz). As compared to the control, in the cortex and hippocampus of rats of melatonin group, we also found a significant reduction of both total and functional activity of Ca2+/calmodulin-dependent protein kinase II (CAMK II) after audiogenic kindling. On the contrary, melatonin administration within the 1st to 7th PND and the 14th to the 21st PND resulted in a decrease in seizure activity. In the first case, both the total (cortical) and functional (hippocampal) CAMK II activities in melatonin-injected rats were increased as compared to control, whereas in the second case, only a slight increase in Ca2+-independent CAMK II activity in the hippocampus of melatonin-injected rats was observed. Probably, the melatonin administration in the period of early postnatal development changes the features of expression and/or regulation of CAMK II activity, and this could be one of the mechanisms of audiogenic seizure modulation in KM rats.