Chimeric potassium channels KcsA-Kv1, which are among the most intensively studied hybrid membrane proteins to date, were constructed by replacing a part of the pore domain of bacterial potassium channel KcsA (K channel of streptomyces A) with corresponding regions of the mammalian voltage-gated potassium channels belonging to the Kv1 subfamily. In this way, the pore blocker binding site of Kv1 channels was transferred to KcsA, opening up possibility to use the obtained hybrids as receptors of Kv1-channel pore blockers of different origin. In this review the recent progress in KcsA-Kv1 channel design and applications is discussed with a focus on the development of new assays for studying interactions of pore blockers with the channels. A summary of experimental data is presented demonstrating that hybrid channels reproduce the blocker-binding profiles of parental Kv1 channels. It is overviewed how the KcsA-Kv1 chimeras are used to get new insight into the structure of potassium channels, to determine molecular basis for high affinity and selectivity of binding of peptide blockers to Kv1 channels, as well as to identify new peptide ligands.