JNJ-39758979 dihydrochloride is a selective, orally active, and high-affinity histamine H 4 receptor antagonist, with K i s of 12.5, 5.3, and 25 nM for human, mouse, and monkey histamine H 4 receptor, respectively. JNJ-39758979 dihydrochloride functionally antagonizes histamine-induced cAMP inhibition with a pA2 of 7.9 in transfected cells. JNJ-39758979 dihydrochloride shows good anti-inflammatory and antipruritic activity.