First they evangelised the Assyrians and later worked in north-west Iran, in a region called Rezaieh.
The missionaries wanted to revitalise the old churches, but their members who converted to Protestantism were forced to leave their old denominations.
Meanwhile, these Presbyterian missionaries' ministry led to the formation of congregations from Armenian Christian, Muslim, Judaism, and Zoroastrian background.
In 1934 the Synod of the Evangelical Church in Iran was formed.
The common language is Persian, Armenian and Assyrian are also used.