[1] On January 5, 1983, Pope John Paul II appointed him as auxiliary bishop of Manila with the titular see of Bacanaria.

In his role as auxiliary bishop, Buhain assisted the Archbishop of Manila, Cardinal Jaime Sin, one of the country’s most powerful religious figures, from 1983 to 2003.

[3][better source needed] On October 31, 2003, the Holy See accepted his resignation from his duties as auxiliary bishop of Manila amid continuing allegations of impropriety involving him.

However he cited his role as auxiliary bishop being terminus ad quem or co-terminus with retired Manila archbishop Cardinal Sin as the reason for the resignation.

[1] Buhain died at the Cardinal Santos Medical Center in San Juan, Metro Manila on November 13, 2024, at the age of 87.