Medical professionals are warning lives will be lost if the Federal Government slashes funding for research.

Hundreds of people attended a rally in Perth to voice their anger at what they fear will be a $400 million budget cut.

"Protesters including scientists and medical researchers held signs saying 'Cures not cuts', while one man's sign read 'Medical research saved my life'.

The Australian Medical Association's WA president David Mountain told the crowd the funding cut would be a catastrophe.

"We're here to oppose the destruction of world class research and the loss of Nobel Prize winners," he said.

"We are here to stop the idiocy that will cost future lives and livelihoods."

Lesley Murphy's son has a rare debilitating muscular disease and says any funding cut would end all hopes of a cure.

"We'll be forever branded as short-sighted, selfish and downright foolish, thank you," she said.

The government will not confirm any cuts, but is warning next month's budget will be tough.