BNP Secretary General Mirza Fakhrul Islam Alamgir has flown to Thailand for medical treatment.
A flight of Biman Bangladesh Airlines carrying the BNP leader and his wife Rahat Ara Begum took off from Hazrat Shahjalal International Airport at 11am on Wednesday.
Yunus Ali, Fakhrul's personal assistant, confirmed the matter.
The BNP leader is likely to return home on May 23.
On February 4, Fakhrul went to Singapore for treatment and was admitted in Singapore National University Hospital.