Toyota's petrol-electric Prius has passed the ultimate "blood test" - performing a potentially life-saving role as a long-haul courier vehicle for Australia's oldest established private pathology practice.

The Prius hybrids are used to transport urgent blood supplies, tissue samples and test results between eight laboratories and more than 100 collection depots in cities and regional centres.

The fuel-efficient Prius hatchbacks are part of an exclusively Toyota fleet of 120 vehicles operated by Melbourne Pathology, which services more than one million patients each year.

The company's fleet manager Blair Loveday said the first Prius entered its 24-hour courier service in 2005.

One Prius had clocked up around 300,000km and others had travelled 120,000km in just 12 months.

"We use Prius on our high-kilometre runs and all the indications are that they are bullet-proof," Mr Loveday said.

"Reliability is vital in our business. It's not unusual to have several urgent bookings at the same time. If we don't get there on time, people can die."

Mr Loveday said a typical courier journey involved an eight-hour round trip twice a day, Monday to Friday.

"Importantly, our drivers love the Prius. The acceleration when you're overtaking is very powerful, and they sit solidly on the road," he said.

Melbourne Pathology is part of the Australian-owned Sonic Healthcare group, one of the world's largest diagnostic medical companies.

Its services reach more than 5,000 private and public hospital beds, specialists and general practitioners as well as various corporate, industrial and institutional clients.