Based on the structure-activity analysis of two series of blockers of the small conductance Ca 2 + -activated K + (SK C a ) channel, a novel class of bis-quinolinium cyclophane blockers has been designed and synthesised. These compounds exhibit submicromolar activity; UCL 1530 (4) is a useful agent since it has been shown (elsewhere) to be selective for the neuronal SK C a channel (IC 5 0 = 80 nM) relative to hepatocyte channels.