The dead men were found in an apartment on Götgatan on the central Stockholm island of Södermalm at around 6.30pm on Friday evening.
Police and emergency services were called to the scene by neighbours who had reacted to a disturbance in the stairwell in the building.
“It was very unpleasant actually even more so now that it has emerged that two people died there,” a neighbour in the building said.
When police arrived at the scene they found the door to the apartment forced open and the two dead men inside.
“At 7pm we launched a murder investigation,” Stockholm police spokesperson Tow Hägg said.
According to news agency TT the victims are reported to be previously known to the police and fingerprints taken from the scene will shortly confirm their identities.
Police have begun interviews with neighbours and potential witnesses and a forensic examination of the apartment is ongoing. Later on Saturday police will examine surveillance camera footage of the area.
According to the website Kriminalen.se the two dead men were shot.
At lunchtime on Saturday police had few clues or lines of inquiry to pursue.
“We have very little to go on. We have no suspects and do not know if it concerns one or more perpetrators,” Bengt Hellström at Södermalm police said.