In laboratory tests, two sweetgrass compounds drove mosquitoes away from tantalising fake blood samples, just as well as the widely-used repellent Deet.
Further tests are needed to see how long the effects last.
The researchers say folk remedies are a rich source of possible new repellents.
"This is the fourth plant that we've investigated in this manner," said Charles Cantrell, a research chemist who works for the US Department of Agriculture.
"The neat thing about this one is that it produces a compound, coumarin, which has a great odour and was known... to have some repelling properties. And it's very safe."
Dr Cantrell was speaking in Boston at the 250th national meeting of the American Chemical Society.
"There's an interesting story about coumarin," he told journalists at the conference.
"Back in the 90s, Avon 'Skin So Soft' had a product that people discovered actually worked well as an insect repellent. It wasn't marketed as an insect repellent, but the effectiveness was well-known among consumers.
"Scientists did an investigation and one of the constituents in Skin So Soft was coumarin - which we've now isolated from sweetgrass."
Despite this, coumarin is not currently registered or marketed as a repellent, Dr Cantrell said.
The second key ingredient he and his colleagues identified in sweetgrass was phytol, a common constituent in essential oils from plants. Phytol, similarly, is known to repel insects but is not currently marketed for that purpose.
Dr Cantrell's team isolated these chemicals from the grass by passing steam through it, separating the oily and volatile compounds and then further purifying them into 12 fractions.
Those 12 samples were presented to mosquitoes in a special test.
"The bioassay is designed to mimic human skin," Dr Cantrell explained. "You put a blood mimic in a little well and cover it with a membrane."
That membrane is then perfumed with the chemical to be tested, and the researchers simply count the bites.
"We'll have five mosquitoes per little chamber. You can watch them bite the membrane, but for final confirmation... you squash them, to see which ones contain the red dye."
Once these results were in, the team identified the specific molecules involved using spectrometry.
Coumarin and phytol were the stand-outs, Dr Cantrell said.
"In this three minute time-frame, measuring the number of bites, they were just as effective as Deet."
The next step is to test them over a more practical timeframe.
"We don't know yet what the duration of repellency is. It may work well in our bioassay for three minutes, but how does it work for three hours?
"These are questions that we're going to try to answer over the next year or two."
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Caroline Wootton-Thomas, 49, forged colleague's signatures on cheques and transferred cash to a bank account she set up in her mother's name.
She used the council's Child Protection Unit petty cash fund for debts, expensive gifts and luxury holidays.
A Cardiff Crown Court jury convicted Wootton-Thomas, of Newport, of theft and transferring criminal property.
The court heard she had asked to be put in charge of the petty cash fund which was meant to be used to cover fuel and parking costs.
The grandmother was caught after a bank statement was sent to the wrong department.
She denied any wrongdoing and blamed her colleagues for stealing the money, which the jury rejected.
Matthew Roberts, prosecuting, said Wootton-Thomas had shown an "arrogance" which culminated in her mother also being charged with money laundering, though she was cleared at trial.
Judge Neil Bidder said: "You have manipulated your mother in the most unscrupulous way. You took out a loan in her name to pay off your debts.
"I've observed fake tears and not a jot of remorse for casting suspicion against other members of your team.
"I regard the fact this money was reserved for vulnerable children to be an aggravating factor."
A hearing in May will set out how she will be able to pay back the money.
US scientists have identified the chemicals responsible for the mosquito-repelling activity of sweetgrass, a plant traditionally used by some Native Americans to fend off the bugs.
[NEXT_CONCEPT]
A Cardiff council worker who stole £35,000 from a children's fund has been jailed for two and a half years.