Bono's voice cracked today as he tried to explain the emotions
he felt talking to a group of mothers infected with the AIDS virus.
"This is an amazing place, amazing people," he said at the prenatal HIV clinic at Soweto's Mr Chris Hani Baragwaneth hospital. "This is very, very hard for an Irish rock star to admit. I'm actually speechless."
Bono and US Treasury Secretary Mr Paul O'Neill met with some of the patients who are among the 4.7 million people infected with HIV in South Africa as part of their 10-day tour of the continent.
Later Bono, the lead singer of U2, gave an impromptu performance at a shanty town in Soweto.
A group of students had begun doing a dance to the U2 song I Still Haven't Found What I'm Looking For.
When their radio broke, Bono continued the song accompanied by claps and a man playing a traditional drum.
Bono and O'Neill were touring several African countries in what has been billed as a fact-finding mission by the US Treasury, and as an exercise in persuasion by the rock legend.
The tour is the result of a meeting a year ago when the two men met in Mr O'Neill's office. Initially reluctant to meet, Mr O'Neill later said he was impressed by the singer's knowledge about Africa.
Bono has said he was determined to show Mr O'Neill that aid can be put to good use in Africa.
Both men hoped the tour will bring worldwide attention to the devastation HIV is bringing to Africa. Mr O'Neill said he was astounded to find out that so much of aid money coming into the country was being used for prevention instead of treatment.
"There is something wrong when the system does not take care of the here and now," he said.
Mr O'Neill's recommendation that treatment come before prevention flies in the face of most Aids programmes around the world that make preventing more infections the top priority.