Footage of isolated tribespeople emerging from the Amazon rainforest and making contact with the wider world has raised concerns about the wellbeing of the group.
Brazil's indigenous authority released video of the meeting along the banks of the Envira River, near the Peruvian border.
The tribespeople are wearing loincloths and carrying bows and arrows and were said to be whistling and making animal sounds. In one incident two of the natives were offered bananas. They appeared wary but quickly grabbed the fruit before retreating out of arm's reach.
It was thought the indigenous people crossed the border from Peru under pressure from illegal logging and drug trafficking.
The first contact was made on June 26, then a team from Brazil's National Indian Foundation travelled to the area and filmed a second encounter on June 30.
The people were identified as members of a group known as the Rio Xinane. They made contact with the Ashaninka native people of northern Brazil.
An interpreter said they had come in search of weapons and allies. "They described being attacked by non-native people and many died after coming down with the flu and diptheria," interpreter Jaminawa Jose Correia said.
Anthropologist Terri Aquino said the group probably wanted axes, knives and pots.
"It's important in their lives because there's an internal war among them and because of contact with non-indigenous groups," he said.
The Indian foundation said the visiting group had returned to the forest because members contracted the flu. A government medical team had been sent to treat seven members of the group.
Rights group Survival International said the incident was extremely worrying, as influenza epidemics had wiped out whole tribes.