Most married couples have experienced ennui in their relationship, a straw poll by a matchmaking firm finds.

The online poll of around 400 married men and women found that 68.5 percent had suffered ennui, and half of them said it set in between the fifth and seventh year of marriage, giving credence to the old wives' tale of the seven-year itch.

The reason cited by the largest group was that they grew tired of their long-term relationship, while others said they stopped treating each other as courteously as they once had. Differences about family values and personality clashes were also frequently mentioned.

Men felt their wives' waning sexual passion was a sing of ennui, and women cited increasing arguments and clashes.

"Ennui in marriage does not necessarily stem from cracks in the marriage. It can signal the personal slump of one spouse," an expert says. "So couples should try to be considerate and open hearts to each other."