Two women working at a nursery near the corner of Big Ranch Road and Oak Knoll Avenue, north of the city of Napa, had a reaction to a chemical that drifted near them, city of Napa spokesman Barry Martin said.
Napa County sheriff's Capt. Tracey Stuart said the sheriff's office first responded to the situation at 8:42 a.m.
She said first responders initially thought the women had been exposed to sulfur, but now believe it may have been pesticides used by nearby vineyards.
Napa County fire crews decontaminated the two workers before they were taken to Queen of the Valley Medical Center in Napa, Martin said.
Stuart said the women were experiencing respiratory problems.
The women were conscious and responsive, Martin said. He did not know if they had since been released from the hospital.
No other people were exposed to the chemical, which was being applied in what may have been a vine nursery, Martin said.