Police are trying to find out what killed four people who were found dead in a detached house in a quiet cul-de-sac.
Officers were called to the street near the centre of Pudsey, Leeds, late on Sunday afternoon.
The area was sealed off while the property in Sheridan Way was checked for harmful chemicals or gases.
A police car was parked outside the modern house, which has a garage on the ground floor. The only other sign of any incident was a smashed lounge window.
Family pictures could be seen inside. Two cars remained on the drive.
Emergency services were called to the property at 5.30pm on Sunday and found the bodies. Ambulance crews also sent a hazardous area response team.
A West Yorkshire Police spokeswoman said: "At around 5.30pm, police were called to a property in the Pudsey area of Leeds following the discovery of four bodies.
"Inquiries are at an early stage and police have sealed off the area while the property is checked for any harmful chemicals or gases."
A Yorkshire Ambulance Service spokeswoman confirmed crews had been called to an address in Pudsey at 5.39pm. She said the hazardous area response team had been sent to the scene.
Fire crews also attended the incident, a spokeswoman for the West Yorkshire Fire and Rescue Service.