1. Anticonvulsants: phenytoin, phenobarbital, carbamazepine and valium at concentrations of 10-100 microM had a significantly inhibitory effect on both K+-stimulated Ca2+-uptake and 32Pi incorporation into phospholipids of rat cortical synaptosomes. 2. Other anticonvulsant, valproic acid, at concentration upto 100 microM had no effect on these two events. 3. Our results suggest that there is a link between Ca2+-influx and polyphosphoinositide turnover in synaptosomes, and this link may relate to the inhibitory effect of these drugs on neurotransmitter release mechanisms of this preparation.