A series of N-[3-(5H-dibenzo[a, d]cyclohepten-5-ylidene)propyl]-N-methylamino- (6a) and N-[3-(6H-dibenz-[b, e]oxepin-11-ylidene)propyl]-N-methylamino-alkanoic acid derivatives (6b) and related compounds (6c-f) were synthesized and examined for pharmacological activities in vitro, i.e., inhibitory effect on monoamine [noradrenaline (NA) and 5-hydroxytryptamine (5-HT)] uptake, inhibitory effect on 5-HT-, histamine-, acetylcholine- and NA-induced contraction, and binding affinity for α₂-adrenoceptor and dopamine D₂-receptor. In vitro tests indicated that zwitter-ionization was capable of maintaining H₁-antihistaminic activity while greatly reducing other pharmacological activities. Further, 6a-f showed much stonger inhibitory effects on compound 48/80-induced lethality in rats than did the corresponding N, N-dimethylamines (2a-f). 3-[N-[3-(6H-Dibenz[b, e]oxepin-11-ylidene)propyl]-N-methylamino]-propionic acid (6b-2), selected as a candidate antiallergic agent of a new type, equally potent in rats and guinea-pigs, exhibited strong inhibitory effects on 48 h homologous passive cutaneous anaphylaxis (PCA) in rats (ED₅₀=0.019 mg/kg, p.o.) and on histamine-induced bronchoconstriction in anesthetized guinea-pigs (ED₅₀=0.0067 mg/kg, p.o.).