The technique, carried out on the thumbnail-sized frogs in Sydney and Melbourne, involves injecting the males and females with a synthetic hormone under the skin.

Eggs are then collected by gently squeezing the females – sperm are obtained by placing a catheter into a male's cloaca, or rear opening.

This was one of the trickier aspects of the method, said Phil Byrne, a biologist carrying out the IVF for the NSW Department of Environment and Climate Change.

"They're tiny little frogs," said Dr Byrne, of Monash University. "It's better if you have small hands."

To mimic natural processes during the frogs' "nuptial embrace" the sperm are then squirted with force onto the eggs in the laboratory.

Dr Byrne and his colleague, Aimee Silla, of the University of Western Australia, had initial success in a pilot study of IVF on corroboree frogs in Melbourne earlier in the year.

About a dozen IVF embryos were obtained.

"We got fertilisation, which was exciting. But the embryos failed during the early stages of development," Dr Byrne said.

For the past fortnight the two scientists have carried out IVF with a further 38 corroboree frogs bred in captivity at Taronga Zoo, but no embryos have formed, Dr Byrne said yesterday.

A Department of Environment scientist, David Hunter, said the development of frog IVF was part of a multi-pronged strategy to try to save the southern corroboree species, which is found only in Kosciuszko National Park.

"Scientists believe its sudden and dramatic decline is due largely to the effects of a fungus known as the amphibian chytrid, which has devastated frogs worldwide," Dr Hunter said.

Installation of 25 large plastic breeding ponds at five sites in the park began last month.

Eggs collected in the wild will be placed in the ponds to grow in fungus-free water until the corroboree frogs are big enough to hop out.

In addition to the Taronga captive breeding program, there are three in Victoria, which release frogs back into the park. However, breeding rates are lower than in nature.

"IVF offers the prospect of improving our captive breeding success," Dr Hunter said.

Dr Byrne said they want to test whether it is better to raise the IVF frog embryos on sphagnum moss, as in the wild, and will try to refine the hormone injections so the males and females release their eggs and sperm simultaneously.

"Timing is everything."