Local anesthetics (LAs) inhibit membrane depolarization by reducing sodium and potassium conductance, and subsequent displacement of calcium ions from binding sites seems to occur. Histamine release appears to be a secretory process in which calcium couples the stimulus to the exocytosis of histamine-containing granules. Furthermore, LAs are structurally similar to histamine H1-receptor antagonists. Thus, LAs can be considered antihistaminic drugs.Previous pharmacological investigations have shown strong local anesthetic, anti-inflammatory and analgesic activity of the carane derivative KP-23. As it has previously been demonstrated that KP-23R, S and its R, S-diasteroisomers have an inhibitory effect on guinea pig ileum contractions, the aim of the present study was to determine and compare the antihistaminic effects of KP-23R, S and its individual isomers KP-23R and KP-23S on isolated guinea pig ileum.