NEW MATERIAL: The indole derivative of formula I [wherein A is 1-12C straight or branched alkyl which is optionally substituted by 3-8C cycloalkyl, halogen, hydroxyl, -CO-NH-SO2-R1 (wherein R1 is 6-10C aryl), etc.; B is 12-18C straight or branched alkyl, alkenyl, alkynyl, 6-10C aryl; D, E, F and G are each H, halogen, cyano, etc., or 3-8C cycloalkyl, or 5- to 7-membered saturated, unsaturated heterocyclic ring, etc., with four hetero atoms selected from the group consisting of O, S, etc.], or its salt.

EXAMPLE: Methyl 3-formyl-6-indolecarboxylate.

USE: Especially useful as a leukotriene antagonist and effective in, e.g. treatment or prophylaxis of allergy, asthma, edema, etc.

PROCESS: The aldehyde of formula II is allowed to react with the phosphorus compounds of formula III, formula IV and formula V to obtain the compound of formula I.