Previous results showed that the KChIP1b splice variant induced slow recovery from inactivation on Kv4.2 whereas KChIP1a enhanced the recovery. As both splice variants only differ by the insertion of the exon1b, an exon rich in aromatic residues, we investigated the role of the aromatic cluster in the slowing of the recovery from inactivation. By substituting aromatic residues individually or in combination we were able to confer KChIP1a recovery behavior to KChIP1b. The substitution of a single or two aromatic residues resulted in an partial restitution of the KChIP1a recovery behavior. However, when three aromatic residues were eliminated in the exon 1b of KChIP1b a fast recovery from inactivation, comparable to the values obtained in the presence of KChIP1a, was obtained. It thus seems that the aromatic cluster modulates the recovery from inactivation by slowing the recovery from one inactivated state. Further investigation will allow the identification of residues involved in the modulation of the closed state inactivation.