Police are treating the deaths of an adult and child in Merthyr Tydfil as unexplained.
The bodies, believed to be those of a woman and child, were found at a house in Church Street, Troedyrhiw, at around 4.20pm on Wednesday.
South Wales Police says next of kin have been informed and post mortem examinations are being arranged. An incident room has been set up at Cardiff Central Police Station.
Troedyrhiw is a close-knit community in Merthyr Tydfil and local people are obviously shocked. We have a team of officers at the scene and in the community looking for information that may assist our enquiries.
We would like to hear from anyone who has seen or heard anything suspicious or unusual in Church Street in recent weeks. The information may seem insignificant but could be important to the investigation.
Detectives are investigating the circumstances leading up to the discovery of the bodies yesterday afternoon. Anyone with information is asked to call 101 or Crimestoppers anonymously on 0800 555111.
Joanne Thomas and her four-month-old baby Harper were found dead at their home in Merthyr Tydfil in July. An open verdict has been recorded.
Police add there is 'no evidence to date' to suggest carbon monoxide killed the two, believed to be a mother and her four-month-old baby.