Police were called to a property in Preston following reports that a woman had jumped from an upstairs window, say police.
She was found by police shortly after 7.40am today with leg and head injuries on Lauderdale Street.
A man at a property Fishergate Hill was found with a head injury and arm wound and was arrested on suspicion of affray.
A spokesman for Lancashire Police said: "At around 7.40am officers attended an address on Fishergate Hill and a woman, 37, was seen jumping out of an upstairs window. She was found shortly after on nearby Lauderdale Street with a leg and head injury.
"A 41-year-old man at the Fishergate Hill address was found with a suspected head injury and a wound to his arm.
"Both were taken to Royal Preston Hospital to be treated. The man has since been arrested on suspicion of affray and is in police custody while the woman remains in hospital.
"Enquiries are on-going to establish what happened in the lead up to the incident and how they have come about their injuries."
Anyone with information is asked to call police on 101 quoting incident reference 192 of Thursday, March 30).