Experiments on rats were carried out to study the effects of administration of delta-sleep-inducing peptide (DSIP) and its analogs (9-14) into the reticular part of the substantia nigra and ventral hippocampus on picrotoxin- and kainate-induced epileptic activity. Additionally, the uptake of [3H]tryptophan by brain structures was studied. Intranigral and intrahippocampal microinjections of peptide and its analogs were found to have anticonvulsant effects against both picrotoxin- and kainate-induced epileptic activity. Studies of the effects of DSIP and its structural analogs on the uptake of tryptophan by brain structures showed that peptides predominantly increased uptake of this amino acid. It is suggested that brain structures which modulate tryptophan uptake are largely responsible for the anticonvulsant actions of DSIP and its analogs. The results obtained here provide evidence that the serotoninergic system is not of key importance in mediating the anticonvulsant effects of DSIP and its analogs.